What allowed the rough riders to be so easily trained before being sent to cuba?

The Rough Riders were well equipped and eager to join the voluntary cavalry group.  Many had previous experience with law enforcement or combat.  

Explanation:

The Rough Riders were voluntary cavalry in the Spanish-American War. They were a group of cowboys, miners, and Native Americans who were already skilled at riding horses and a number had experienced some form of combat previously. This is why there were Texas Rangers as volunteers, for example.  Also they were well equipped for a voluntary regimen thanks to lobbying by Lieutenant Colonel Theodore Roosevelt. It also seems the group were eager to volunteer as the call to recruit 125 000 men was easily met.

d.he wanted to send diplomats to communist countries.