As you may know, Panama was once a Columbian Province until Teddy Roosevelt aided Panamanian rebels in their effort for independance. The payoff for the US was the Panama Canal. After the Panamanians declared independance, the US sent gunboats to Panama City and Colon, thereby making Columbian intervention via the sea an impossibility. The Columbian government then tried to send a large force of men into Panama through the the Darién Gap. The force, which consisted of Columbian military men acclimated to tropical conditions, was decimated by yellow fever in the Gap, and went back to Columbia en masse.