After the death of his step-brother Dan I, Mircea takes over the throne in 1386, as Wallachia, on one side, was going through a process of economic, administrative, religious development, but also of strengthening the army, and on the other side it was confronted with the expansion tendencies of the Hungarian Kingdom and Poland, which were aiming at controlling the mouths of the Danube, but also those of the Ottoman Empire in the Balkans.

[4] Mircea was the son of voivode Radu I of Wallachia and his wife, Doamna Calinichia,[5] thus being a descendant of the House of Basarab.

Found in a volatile region of the world, this principality's borders constantly shifted, but during Mircea's rule, Wallachia controlled the largest area in its history: from the Southern Carpathians in the north to the Danube in the south, and from today's Iron Gates on the Danube in the west to the Black Sea in the east.

He fortified the Danube citadels and strengthened "the great army" made up of townspeople and of free and dependent peasants.

[citation needed] Through the intermediary of Petru Mușat, the prince of Moldavia, he concluded a treaty of alliance with Władysław II Jagiełło, king of Poland in 1389.

[11] He maintained close relations with Sigismund of Luxembourg, the king of Hungary, relying on their common interest in the struggle against Ottoman expansion.

[12][13] His interventions in support of the Bulgarians south of the Danube who were fighting against the Turks brought him into conflict with the Ottoman Empire.

He chose to fight what would now be called a guerrilla war, by starving the opposing army and using small, localized attacks and retreats (a typical form of asymmetric warfare).

[18] The defeat of Sultan Beyazid I by Timur Lenk (Tamerlane) at Ankara in the summer of 1402 opened a period of anarchy in the Ottoman Empire and Mircea took advantage of it to organize together with the Hungarian king a campaign against the Turks.