Because of too many 'join the EU/leave the EU' results, I have included the second result where applicable.

Results are from Athens, Greece.

Why did ... Albania leave the Warsaw pact
            Andorra declare war on Germany
            Armenia and Azerbaijan go to war
            Austria declare war on Serbia
            Azerbaijan lose the war
            Belarus leave the Soviet Union
            Belgium join WW1
            Bosnia and Serbia fight
            Bulgaria join WW1
            Croatia join the EU - attack Bosnia
            Cyprus join the EU - leave the British empire
            Czech Republic change its name
            Denmark ban marmite
            Estonia join the EU - sink
            Finland join the EU - fight with the Nazis
            France veto Britain
            Georgia secede from the Union
            Germany lose WW1
            Greece fall
            Hungary join the EU - enter WW2
            Iceland not join the EU - ban beer
            Ireland split
            Italy invade Greece
            Kazakhstan change its capital
            Kosovo declare independence
            Latvia join the EU - join the euro
            Liechtenstein become a country
            Lithuania join the EU - challenge Russia
            Luxembourg join the EU - move to Switzerland in 1889
            Macedonia (FYROM) conquer Greece
            Malta join the EU - get the George Cross
            Moldova leave Romania
            Monaco coin crash
            Montenegro join NATO
            Netherlands colonize Indonesia
            Norway not join the EU - knight a penguin
            Poland join the EU - become communist
            Portugal explore
            Romania join the Axis
            Russia leave WW1
            San Marino not join Italy
            Serbia join WW1
            Slovakia join the EU - and Czech split
            Slovenia and Croatia declare independence
            Spain create missions in the colonies
            Sweden join the EU - ban Christmas lights
            Switzerland join WW1
            Turkey invade Cyprus
            Ukraine shot down MH17
            United Kingdom (UK) leave EU - join EU
            Vatican City (Holy See) become a country