Period of expansion:

Timur spent the next 35 years in various wars and expeditions. He not only consolidated his rule at home by the subjugation of his foes, but sought extension of territory by encroachments upon the lands of foreign potentates. His conquests to the west and northwest led him to the lands near the Caspian Sea and to the banks of the Ural and the Volga. Conquests in the south and south-West encompassed almost every province in Persia, including Baghdad, Karbala and Northern Iraq.

One of the most formidable of Timur's opponents was another Mongol ruler, a descendant of Genghis Khan named Tokhtamysh. After having been a refugee in Timur's court, Tokhtamysh became ruler both of the eastern Kipchak and the Golden Horde. After his accession, he quarreled with Timur over the possession of Khwarizm and Azerbaijan. However, Timur still supported him against the Russians and in 1382 Tokhtamysh invaded the Muscovite dominion and burned Moscow.

Orthodox tradition states that later, in 1395 Timur, having reached the frontier of Principality of Ryazan, had taken Elets and started advancing towards Moscow. Great Prince Vasily I of Moscow went with an army to Kolomna and halted at the banks of the Oka River. The clergy brought the famed Theotokos of Vladimir icon from Vladimir to Moscow. Along the way people prayed kneeling: “O Mother of God, save the land of Russia!” Suddenly, Timur's armies retreated. In memory of this miraculous deliverance of the Russian land from Timur on 26 August, the all-Russian celebration in honor of the Meeting of the Vladimir Icon of the Most Holy Mother of God was established.

Conquest of Persia:

After the death of Abu Sa'id, ruler of the Ilkhanate, in 1335, there was a power vacuum in Persia. In the end, Persia was split amongst the Muzaffarids, Kartids, Eretnids, Chobanids, Injuids, Jalayirids, and Sarbadars. In 1383, Timur started his lengthy military conquest of Persia, though he already ruled over much of Persian Khorasan by 1381, after Khwaja Mas'ud, of the Sarbadar dynasty surrendered. Timur began his Persian campaign with Herat, capital of the Kartid dynasty. When Herat did not surrender he reduced the city to rubble and massacred most of its citizens; it remained in ruins until Shah Rukh ordered its reconstruction. Timur then sent a General to capture rebellious Kandahar. With the capture of Herat the Kartid kingdom surrendered and became vassals of Timur; it would later be annexed outright less than a decade later in 1389 by Timur's son Miran Shah.

Timur then headed west to capture the Zagros Mountains, passing through Mazandaran. During his travel through the north of Persia, he captured the then town of Tehran, which surrendered and was thus treated mercifully. He laid siege to Soltaniyeh in 1384. Khorasan revolted one year later, so Timur destroyed Isfizar, and the prisoners were cemented into the walls alive. The next year the kingdom of Sistan, under the Mihrabanid dynasty, was ravaged, and its capital at Zaranj was destroyed. Timur then returned to his capital of Samarkand, where he began planning for his Georgian campaign and Golden Horde invasion. In 1386, Timur passed through Mazandaran as he had when trying to capture the Zagros. He went near the city of Soltaniyeh, which he had previously captured but instead turned north and captured Tabriz with little resistance, along with Maragha. He ordered heavy taxation of the people, which was collected by Adil Aqa, who was also given control over Soltaniyeh. Adil was later executed because Timur suspected him of corruption.

Timur then went north to begin his Georgian and Golden Horde campaigns, pausing his full-scale invasion of Persia. When he returned, he found his generals had done well in protecting the cities and lands he had conquered in Persia. Though many rebelled, and his son Miran Shah, who may have been regent, was forced to annex rebellious vassal dynasties, his holdings remained. So he proceeded to capture the rest of Persia, specifically the two major southern cities of Isfahan and Shiraz. When he arrived with his army at Isfahan in 1387, the city immediately surrendered; he treated it with relative mercy as he normally did with cities that surrendered (unlike Herat). However, after Isfahan revolted against Timur's taxes by killing the tax collectors and some of Timur's soldiers, he ordered the massacre of the city's citizens; the death toll is reckoned at between 100,000 and 200,000. An eye-witness counted more than 28 towers constructed of about 1,500 heads each.[58] This has been described as a "systematic use of terror against towns...an integral element of Tamerlane's strategic element", which he viewed as preventing bloodshed by discouraging resistance. His massacres were selective and he spared the artistic and educated. This would later influence the next great Persian conqueror: Nader Shah.

Timur then began a five-year campaign to the west in 1392, attacking Persian Kurdistan. In 1393, Shiraz was captured after surrendering, and the Muzaffarids became vassals of Timur, though prince Shah Mansur rebelled but was defeated, and the Muzafarids were annexed. Shortly after Georgia was devastated so that the Golden Horde could not use it to threaten northern Iran. In the same year, Timur caught Baghdad by surprise in August by marching there in only eight days from Shiraz. Sultan Ahmad Jalayir fled to Syria, where the Mamluk Sultan Barquq protected him and killed Timur's envoys. Timur left the Sarbadar prince Khwaja Mas'ud to govern Baghdad, but he was driven out when Ahmad Jalayir returned. Ahmad was unpopular but got some dangerous help from Qara Yusuf of the Kara Koyunlu; he fled again in 1399, this time to the Ottomans.

Tokhtamysh–Timur war

In the meantime, Tokhtamysh, now khan of the Golden Horde, turned against his patron and in 1385 invaded Azerbaijan. The inevitable response by Timur resulted in the Tokhtamysh–Timur war. In the initial stage of the war, Timur won a victory at the Battle of the Kondurcha River. After the battle Tokhtamysh and some of his army were allowed to escape. After Tokhtamysh's initial defeat, Timur invaded Muscovy to the north of Tokhtamysh's holdings. Timur's army burned Ryazan and advanced on Moscow. He was pulled away before reaching the Oka River by Tokhtamysh's renewed campaign in the south.

In the first phase of the conflict with Tokhtamysh, Timur led an army of over 100,000 men north for more than 700 miles into the steppe. He then rode west about 1,000 miles advancing in a front more than 10 miles wide. During this advance, Timur's army got far enough north to be in a region of very long summer days causing complaints by his Muslim soldiers about keeping a long schedule of prayers. It was then that Tokhtamysh's army was boxed in against the east bank of the Volga River in the Orenburg region and destroyed at the Battle of the Kondurcha River, in 1391.

In the second phase of the conflict, Timur took a different route against the enemy by invading the realm of Tokhtamysh via the Caucasus region. In 1395, Timur defeated Tokhtamysh in the Battle of the Terek River, concluding the struggle between the two monarchs. Tokhtamysh was unable to restore his power or prestige, and he was killed about a decade later in the area of present-day Tyumen. During the course of Timur's campaigns, his army destroyed Sarai, the capital of the Golden Horde, and Astrakhan, subsequently disrupting the Golden Horde's Silk Road. The Golden Horde no longer held power after their losses to Timur.

Ismailis

In May 1393, Timur's army invaded the Anjudan, crippling the Ismaili village only a year after his assault on the Ismailis in Mazandaran. The village was prepared for the attack, evidenced by its fortress and system of tunnels. Undeterred, Timur's soldiers flooded the tunnels by cutting into a channel overhead. Timur's reasons for attacking this village are not yet well understood. However, it has been suggested that his religious persuasions and view of himself as an executor of divine will may have contributed to his motivations. The Persian historian Khwandamir explains that an Ismaili presence was growing more politically powerful in Persian Iraq. A group of locals in the region was dissatisfied with this and, Khwandamir writes, these locals assembled and brought up their complaint with Timur, possibly provoking his attack on the Ismailis there.

Campaign against the Tughlaq dynasty:

In 1398, Timur invaded northern India, attacking the Delhi Sultanate ruled by Sultan Nasir-ud-Din Mahmud Shah Tughluq of the Tughlaq dynasty. After crossing the Indus River on 30 September 1398, he sacked Tulamba and massacred its inhabitants. Then he advanced and captured Multan by October. His invasion was unopposed as most of the Indian nobility surrendered without a fight, however he did encounter resistance from the united army of Rajputs and Muslims at Bhatner under the command of Rao Dul Chand, the Rao initially opposed Timur but when hard-pressed he considered surrender. He was locked outside the walls of Bhatner by his brother and was later killed by Timur. The garrison of Bhatner then fought and were slaughtered to the last man. Bhatner was looted and burned to the ground.

While on his march towards Delhi, Timur was opposed by the Jat peasantry, who would loot caravans and then disappear in the forests, Timur had 2,000 Jats killed and many taken captive.[69][70] But the Sultanate at Delhi did nothing to stop his advance.

Capture of Delhi (1398)

The battle took place on 17 December 1398. Sultan Nasir-ud-Din Mahmud Shah Tughluq and the army of Mallu Iqbal[72] had war elephants armored with chain mail and poison on their tusks.[9]:267 As his Tatar forces were afraid of the elephants, Timur ordered his men to dig a trench in front of their positions. Timur then loaded his camels with as much wood and hay as they could carry. When the war elephants charged, Timur set the hay on fire and prodded the camels with iron sticks, causing them to charge at the elephants, howling in pain: Timur had understood that elephants were easily panicked. Faced with the strange spectacle of camels flying straight at them with flames leaping from their backs, the elephants turned around and stampeded back toward their own lines. Timur capitalized on the subsequent disruption in the forces of Nasir-ud-Din Mahmud Shah Tughluq, securing an easy victory. Nasir-ud-Din Mahmud Shah Tughluq fled with remnants of his forces. Delhi was sacked and left in ruins. Before the battle for Delhi, Timur executed 100,000 captives.

The capture of the Delhi Sultanate was one of Timur's greatest victories, as at that time, Delhi was one of the richest cities in the world. After Delhi fell to Timur's army, uprisings by its citizens against the Turkic-Mongols began to occur, causing a retaliatory bloody massacre within the city walls. After three days of citizens uprising within Delhi, it was said that the city reeked of the decomposing bodies of its citizens with their heads being erected like structures and the bodies left as food for the birds by Timur's soldiers. Timur's invasion and destruction of Delhi continued the chaos that was still consuming India, and the city would not be able to recover from the great loss it suffered for almost a century.

Campaigns in the Levant:

Before the end of 1399, Timur started a war with Bayezid I, sultan of the Ottoman Empire, and the Mamluk sultan of Egypt Nasir-ad-Din Faraj. Bayezid began annexing the territory of Turkmen and Muslim rulers in Anatolia. As Timur claimed sovereignty over the Turkoman rulers, they took refuge behind him.

In 1400, Timur invaded Armenia and Georgia. Of the surviving population, more than 60,000 of the local people were captured as slaves, and many districts were depopulated. He also sacked Sivas in Asia Minor.

Then Timur turned his attention to Syria, sacking Aleppo, and Damascus. The city's inhabitants were massacred, except for the artisans, who were deported to Samarkand. Timur cited the killing of Hasan ibn Ali by the Umayyad caliph Muawiyah I and the killing of Husayn ibn Ali by Yazid I as the reason for his massacre of the inhabitants of Damascus.

Timur invaded Baghdad in June 1401. After the capture of the city, 20,000 of its citizens were massacred. Timur ordered that every soldier should return with at least two severed human heads to show him. When they ran out of men to kill, many warriors killed prisoners captured earlier in the campaign, and when they ran out of prisoners to kill, many resorted to beheading their own wives.

Invasion of Anatolia:

In the meantime, years of insulting letters had passed between Timur and Bayezid. Both rulers insulted each other in their own way while Timur preferred to undermine Bayezid's position as a ruler and play down the significance of his military successes.

This is the excerpt from one of Timur's letters addressed to Ottoman sultan:

"Believe me, you are but pismire ant: don't seek to fight the elephants for they'll crush you under their feet. Shall a petty prince such as you are contend with us? But your rodomontades (braggadocio) are not extraordinary; for a Turcoman never spake with judgement. If you don't follow our counsels you will regret it".

Finally, Timur invaded Anatolia and defeated Bayezid in the Battle of Ankara on 20 July 1402. Bayezid was captured in battle and subsequently died in captivity, initiating the twelve-year Ottoman Interregnum period. Timur's stated motivation for attacking Bayezid and the Ottoman Empire was the restoration of Seljuq authority. Timur saw the Seljuks as the rightful rulers of Anatolia as they had been granted rule by Mongol conquerors, illustrating again Timur's interest with Genghizid legitimacy.

In December 1402, Timur besieged and took the city of Smyrna, a stronghold of the Christian Knights Hospitalers, thus he referred to himself as ghazi or "Warrior of Islam". A mass beheading was carried out in Smyrna by Timur's soldiers.

With the Treaty of Gallipoli in February 1402, Timur was furious with the Genoese and Venetians, as their ships ferried the Ottoman army to safety in Thrace. As Lord Kinross reported in The Ottoman Centuries, the Italians preferred the enemy they could handle to the one they could not.

In c. 1402–1403, Bayezid I's son Mehmed Çelebi behaved as Timur's vassal. Beside the other princes, Mehmed minted coin which Timur's name appeared as "Demur Han Gürgân", alongside his own as "Mehmed bin Bayezid han". This was probably an attempt on Mehmed's part to justify to Timur his conquest of Bursa after the Battle of Ulubad. After Mehmed established himself in Rum, Timur had already begun preparations for his return to Central Asia, and took no further steps to interfere with the status quo in Anatolia.

While Timur was still in Anatolia, Qara Yusuf assaulted Baghdad and captured it in 1402. Timur returned to Persia and sent his grandson Abu Bakr ibn Miran Shah to reconquer Baghdad, which he proceeded to do. Timur then spent some time in Ardabil, where he gave Ali Safavi, leader of the Safaviyya, a number of captives. Subsequently, he marched to Khorasan and then to Samarkhand, where he spent nine months celebrating and preparing to invade Mongolia and China.

Attempts to attack the Ming dynasty:

By 1368, Han Chinese forces had driven the Mongols out of China. The first of the new Ming dynasty's emperors, the Hongwu Emperor, and his son, the Yongle Emperor, produced tributary states of many Central Asian countries. The suzerain-vassal relationship between Ming empire and Timurid existed for a long time. In 1394, Hongwu's ambassadors eventually presented Timur with a letter addressing him as a subject. He had the ambassadors Fu An, Guo Ji, and Liu Wei detained. Neither Hongwu's next ambassador, Chen Dewen (1397), nor the delegation announcing the accession of the Yongle Emperor fared any better.

Timur eventually planned to invade China. To this end Timur made an alliance with surviving Mongol tribes based in Mongolia and prepared all the way to Bukhara. Engke Khan sent his grandson Öljei Temür Khan, also known as "Buyanshir Khan" after he converted to Islam while at the court of Timur in Samarkand.