They did not want the states to have all the power
Henry David Thoreau opposed the Mexican War, so you could consider him an opponent of Manifest Destiny. Manifest Destiny was an overarching idea or concept, but it's practical application took place in many different events and contexts.
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The era which most deeply influenced the writing of the Declaration of Independence was the Modern Era and the illuminism movement. The Declaration of Independence was written in 1776, when illumimism movement was at its peak, and its influenced was heavy on the declaration as it emphatiziced the natural rights of the people, for example.
nationalism: it is great to have a sense on national pride and togetherness although if it gets out of hand it can be almost brainwashing and used to control citizens.
militarism: being prepared and having sufficient miliatry resources avalivable can be great IF there is an attack although it can be viewed as intimidating and scare off allies. also it can cause other resources to thin