Which American philosophy most contributed to the "closing" of the Western frontier?

In 3-6 sentences describe the strategy between generals' grant and lee's armies at wilderness and spotslvania . why are they significant? i will mark brainliest! answer only if u truly know the correct answer

Brainliestttme : ) how did the soviet union try to maintain control?

How did the grooms national product (gnp) of the united states change between 1940 and 1944