I think its A the gov can not regulate where
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Caring for Magwitch during his illness and trial.
The usa ended its war in Vietnam due to heavy casualties that resulted topublic outcry in the home country. the USA was in fact reaching a dead end in the jungle as it found itself being heavily assaulted by the Soviet led assaults. There was also the strategic realisation that the USA would better be served by peace with honour as expounded by president Nixon.
1) They needed resources from North America.
2) Wanted to explore unknown lands and possibly colonize there.