There was some resistance in the process, a lot of bloodshed and native lives lost, but a definite gain for America in the end. This resulted in the natives eventually being pushed to live on small reservations and their way of life almost totally diminished. .
In the north pacific, the Oregon Territory was occupied by Britain and highly sought after by the United States. The U.S. Government used their belief in their God-given right to expand its borders as far west as possible to acquire this territory. Originally, then U.S. President James Polk negotiated a border along 54-50 parallel. If Great Britain refused this, Polk proclaimed, all out war would be inevitable to achieve it. Luckily, Great Britain was not interested in war because America was not fully equipped militarily to handle a war with a super power. Britain eventually gave in and allowed America to expand her borders along the 49th parallel. .
Next, the American Government was interested in expanding its borders south of Texas. The issue was that Texas was a part of Mexico being controlled by Spain. At the time Spanish colonies were revolting and seeking their independence which set the stage for American expansion. The only issue is that Great Britain seemed interested in the territory as well for trade purposes. President Monroe stated the doctrine in his State of the Union Address in 1823, which later was coined as the "Monroe Doctrine" in 1850. It stated that any attempt of colonization by European countries in either South or North America would be looked upon as aggressive and would warrant intervention. It also noted that the United States would not interfere with European interests outside of the American continent, including European colonies or internal affairs. This would allow the freedom of Latin American colonies to be influenced by the United States without the interferences of European countries.