In 1803, Thomas Jefferson, made the Louisiana Purchase, which the United States bought from France, for a mere $15 million dollars, all for an area of 827,000 square miles. In 1867, Seward negotiated the terms of the Alaskan purchase from Russia for $7.2 million dollars, for an area of nearly 600,000 square miles. In 1904, the United States purchased what would be known as the Panama Canal from Panama for $10 million dollars, as well as paying France $40 million dollars for the work that they had initiated in the building of the Panama Canal but never finished, for an area of just 435 square miles.
What made the Panama Canal of vital interest to the United States, was the ability of that canal to connect the Atlantic ocean from its great ports such as those in New York City and New Orleans with its great and upcoming ports on the Pacific coast, and onward then to Asian markets as well as to better command those two oceans for the security and the power of the United States, which allowed America thereby to bypass having to sail around South America and therefore saving in distance some 8,000 miles of sea travel. This was of upmost importance in the early 20th century, because aerial power was not yet known, and the great global powers of that age, were all those that controlled the seas, and being able to travel seamlessly from the Pacific to the Atlantic and vice versa, gave America that power, along with increasing its reach and strength in global trade.
When the Panama Canal was successfully completed, at a great cost in both men's lives lost as well as in monies spent, it indisputably help solidify America's status as the greatest economic power in the world, as well as establishing America as the most dominant military force, if not immediately in armaments and in ships, then certainly in its capacity and strategic positioning to be so, which is why when America entered into World War I, the tide of that war immediately changed to the Allies of that cause.
France's failure to successfully complete the massive engineering and manpower needed to create the Panama Canal, was the opportunity for America to take over and thereby to control the Panama Canal for primarily its own purposes, of which, Panama as a country, would best be seen, at that time, as a vassal state to America. However, eventually Panama would assert its sovereignty, through American acquiescence over the Panama Canal, and thereby a new treaty would be signed transferring the canal over to Panama at the end of 1999, with the important provision that America would maintain the right to defend the canal.
America would not be America as we know it today, if it was not for the strategic purchases as well as the taking of lands from other nations, in addition to having the vision and foresight to recognize that the building of the Panama Canal would not only be vital for trade within America, but also for trade with other countries, as well as making America the international powerhouse, second to none.