The “Dress Rehearsal” to WW2 was the Nazis and Italian Fascists bombing cities in *

Spain.

Explanation:

The Spanish Civil War was described as "dress rehearsal", because the bombing of Spanish cities by Nationalist rebels with the support of Nazi Germany and Fascist Italy, allowed them to test new weapons later used in World War II, like the He-111 and Do-17 bombers.

Particularly, gruesome was the bombing of Guernica, later depicted in Pablo Picasso´s painting because it was a military air force attack over civilians, which is considered as a war crime.

d. japan's attack on pearl harbor

alliances in ww1 were different from ww2 because the entente in ww1 made up of serbia,russia,france,britan,japan and italy later america  and all allied in a sort of balance of power and too keep germany,austria-hungary,and the ottomans down. russia allied the serbians in order to exert its influence in the balkans while france allied the russians because france was still in dismay and insulted after the defeat to the germans during the unification of germany and britian allied the belgians after the germans invasion of belgium.in ww2 the alliances were in a preemptive attempt to deter any further wars into happening while germany and italy allied since they were insulted and humiliated after the previous war while also sharing a similar ideology of facsim along with japan which all 3 had a want for world domination and agreed to assist one another in the endevours 

explanation: