Mikhail Gorbachev's reformist policies in the Soviet Union fuelled opposition movements to the Communist regimes in the Soviet bloc countries. The structures of the Eastern bloc disintegrated with the dissolution of the Warsaw Pact and Comecon. The Soviet Union broke up into independent republics.
Britain entered World War I in 1914 to honor a treaty that promised to defend Belgium and to fulfill an alliance with France and Russia. The Germans attacked Liege, Belgium, in the first battle of World War I, and then marched on to attack France.
I'm assuming by "war" you mean World War I
The primary causes were that Sparta feared of the growing power and influence of the Athenian empire
