Third parties make the political system more democratic by offering more choices. America has become a two-party system with third parties struggling to even get on the ballot in most states.
The primary effect of the Dred Scott decision, based only on the option in this list, was that "Congress could not prohibit slavery," but mostly it meant that blacks weren't considered citizens and thus could not sue for their freedom.
After the defeat in WWII, Germany's capital, Berlin was divided into four zones which were separately governed by France,Britain,US and the USSR. In 1946,the three nations merge the zone of France, Britain and US to be governed by one government, USSR strongly protested against it as the merged zones account for 75% of Germany's original population. In reaction,USSR cut off all land routes linking Berlin and the Western zone,claiming that it was to protect USSR's economy. The event was known as Berlin Blockade.