Both of Turkey and Greece were facing a crisis, in where they are being seduced by the ideology of communism and socialism.
Because popular sovereignty was well supported because it allowed the local citizens of a territory to decide if slavery was to be allowed or illegal. Stephen A. Douglas pushed for popular sovereignty during the 1840's.
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It happened right after world war one when Germany was left in ruins due to the war and Hitler proposed a new ideology of Naziism which everyone started to like due to the situation Germany was in at the time.