How was Karl Marx & freidrich engels prediction of communist revolutions played out in real world events?

They were partly correct, and partly incorrect.

They were right when they said that a communist revolution would eventually take place: this is what happened in Russia in 1917, when led by Lenin, a communist government was put in place, which adhered to the ideas of Marx and Engels.

They were wrong when they said that socialism, and eventually communism, would replace capitalism as the dominant economic system. In fact, capitalism is still the dominant economic system in the world, and most of the socialist economies have eventually failed.

answer: president kennedy is vowing to protect freedom in this paragraph.