Why did the United States rise as a world power in the 20th century?

Only the 20th century? In fact, the rise of the United States should start from the civil war, after the end of the civil war. The United States is unified in form, so there is a unified market, and because of the promulgation of the Homestead Law, a large number of land in the west is used. The American economy developed rapidly, and then the United States promulgated the patent law, which can be said to have poured a bucket of gasoline into the small flame of human creativity. Driven by interests, the second industrial revolution rose in the United States. Therefore, driven by new technology, the United States has become a world power. On the other hand, the United States has a unique territorial advantage. There are no strong enemies in the north and south of the east and west oceans. The 6,000-kilometer Atlantic Ocean separates war-torn Europe, and the 9,000-kilometer Pacific Ocean is far away from chaotic Asia. Canada is in the north, the same species and the same language, Mexico is in the south, and 57% of the territory is occupied by the United States. There are Appalachians in the west and Rockies in the south. There will be no mountains, and then a large plain in the middle can be cultivated, so agriculture is extremely developed. In addition, because it is far from the war, the United States does not need the protection of the army and does not need military spending. By the time of World War I, there were only 23,000 troops and no decent weapons and equipment, so the American economy developed rapidly ~ ~