U.S. imperialism in 1865-1914?

It's been a while since i had American History. However my teacher described it this way. The United States wanted to take lands, with resources and other strategic values. The government at the time did this because they where afraid that America was falling behind the other empires. Spain, Britain , and France for example all had large amounts of land and the resources from those lands. If America where to go to war with any of those powers then our limited resources would make it difficult for us to have won.