Other countries entered the on-going civil war and dividedly supported the republican or the nationalists. The German intervention triggered World War II when it supported the Nationalists, while France and Britain supported the Republicans. The military interventions led the countries to war.
Germany provided heavy military training and tactics to the Nationalists that later was formed as the Condor Legion, which led the Nationalists military. The Condor Legion experienced successive victories because of their rigorous training, however, in the end, they were defeated by Britain's army.
Because Americans felt they were a better society and people than other groups of people (Mexicans/Native Americans) already living out West and somehow that justified them taking over the West. The Mexican government grew frustrated with them moving their illegally.
