The Russo-Turkish War of 1877–78 resulted in the formation of the third and current Bulgarian state. Many ethnic Bulgarians were left outside the new nation's borders, which stoked irredentist sentiments that led to several conflicts with its neighbours and alliances with Germany in both world wars. In 1946 Bulgaria came under the Soviet-led Eastern Bloc and became a one-party socialist state. The ruling Communist Party gave up its monopoly on power after the revolutions of 1989 and allowed multiparty elections. Bulgaria then transitioned into a democracy and a market-based economy. Since adopting a democratic constitution in 1991, Bulgaria has been a unitary parliamentary republic composed of 28 provinces, with a high degree of political, administrative, and economic centralisation.