Monroe doctrine
Monroe doctrine warns European countries to not colonize or puppet monarch
The allies point of view was that WW1 was cause by Germany and its allies and that Germany had to be "punished" for it with reparations. These reparations were a source of great dissatisfaction in Germany, contributed to its financial crisis in the period after the War, and paved a way for Hitler's government, because the frustrated and desperate people were more likely to accept an extreme government.
It is false that Communism was the dominant economic force of the twentieth century, although it certainly overtook a great deal of territory. Capitalism was still overall dominant.