He determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers.
The United States wanted to build the Panama Canal in order to save time and money on trading. Before the Panama Canal, people had to sail all the way around Africa in order to get to the other side of the world, which costed much more money and took a lot longer. The US owns the canal because of the Hay-Bunau-Varilla treaty, which gave the rights to the USA to build and manage it.
a steady population of workers and the resources need to get it