D. In order to get and build the Panama Canal.
Hay-Herrán Treaty was signed by Colombia in 1903, granting the United States to use the Isthmus of Panama (Panama was then part of Colombia). The United States wanted to pursue the treaty in order to build the Panama canal which would connect Atlantic to Pacific Ocean. But Colombia backed out from the treaty, so the United States created a plan and helped Panama's separation from Colombia to get ownership of the canal.