The Constitution was written to form a more perfect union, establish justice, insure domestic tranquility, provide for the common defense, promote general welfare, and secure the blessings of liberty to ourselves and our prosperity. (basically it's addressed in the very document itself, The Preamble)
President William McKinley signed a joint resolution annexing Hawaii in 1898, although the islands remained a territory until granted statehood as the fiftieth state in 1959.
Moreover, the Spanish-American War of 1898 forced the Spanish to relinquish claims on Cuba and to cede sovereignty over Guam, Puerto Rico, and the Philippines, securing the position of the United States as a Pacific power.
