Competition over China became fierce and very weak by years of civil wear. Refused in 1800's. Everyone wanted a piece of China, which was called Sphere of Influence. Open Door Police is the secretary of State John Hay writes letters to other nations letting any nations to trade with each other. China also had very cheap labor. Several nations saw Boxer Rebellion as an excuse to seize more land in China. 

Teddy Roosevelt became president in 1901 and he was determine to create a canal through a narrow strip of land with two big huge bodies of water. Knew a canal would be greatly benefit American commerce and military. It would reduce the cost of shipping goods, trade more quickly and make the military more protected then ever. The navy would quickly be able to move ships back and forth, from one place to another, and between the Pacific and Atlantic Ocean. Which I think is pretty cool, then can bring ships wherever they need to get to now. What I thought was cool is that they had to make a deal with Columbia because Panama belonged to Columbia. Panama was Columbia's, and the people want it back. He offered ten million dollars in cash and $250,000 a year just in rent, that is ridiculously expensive in my opinion. And of course Columbia did not except the deal and Teddy becomes furios and starts a panic attack. 

Now Panamanians rebel to get independence from Columbia and Roosevelt supports the rebels and stops Columbia from being stupid and from suppressing the rebellion. Furthermore, in 1903 Panama declars itself as an independent republic.