Which country signed a non-aggression pact with an axis power at the start of the world war ii but later sided with the allies?

The correct answer is: "the URSS".

The URSS and Nazi Germany signed the non-aggresion treaty known as Molotov-Ribbentrop Pact in 1939. The pact was broken in 1941, when Hitler attacked the URSS in the Operation Barbarrosa, initiating the fight on the Eastern European threatre motivated by the sucesses that, up to that point, Germany had accomplished in the Western front.

theodore roosevelt 26th u.s. president : i admire his energy and passion. he was a fundamentally good man, brilliantly intelligent, possessed of extraordinary will and ability, supremely self-confident, bold, egalitarian, idealistic…. , lord, can we have him back?