Why did roosevelt believed the us could not isolate itself from the rest of the world?

He believed that the interdependence today technically and morally prevented us from isolating ourselves. He believed that US had an important role to play in the world but he was unable to realise his internationalist policy during 1930's as the economy was weak and significant number of Americans preferred isolationism. It was Japanese attack on the pearl harbour that drew into conflict with Japan. He also believed that depression arose due to international circumstances. It was due to his internationalist approach that he was able to establish good economic relations with Latin American countries with "good neighbour initiative". It was due to his effort that US supported Us pan-American conference resolution that stipulated non interference in the internal and foreign affairs of other countries.

this means that germany had to pay the allied countries. reparations are/is essentially payment for something that they have done wrong, so after ww1, germany was forced to pay reparations so they could replenish the allied countries resources' that they had lost during the war.