Lithuanian lands were united under MINDAUGAS in 1236; over the next century, Lithuania extended its territory through alliances and conquest to include most of present-day Belarus and Ukraine. By the end of the 14th century, Lithuania was the largest state in Europe. An alliance with Poland in 1386 led the two countries into a union through a common ruler. In 1569, Lithuania and Poland formally united into a single dual state, the Polish-Lithuanian Commonwealth. This entity survived until 1795 when surrounding countries partitioned its remnants. Lithuania regained its independence after World War I, but the USSR annexed it in 1940 -- an action never recognized by the US and many other countries. In 1990, Lithuania became the first of the Soviet republics to declare its independence, but Moscow did not recognize this proclamation until 1991. The last Russian troops withdrew in 1993. Lithuania subsequently restructured its economy for integration into West European institutions; it joined both NATO and the EU in 2004. In 2015, Lithuania joined the euro zone, and it joined the Organization for Economic Cooperation and Development in 2018.