What Business does Washington have in the Philippines?

The U.S. is attempting to move thousands of heavily armed soldiers into the Philippines for the first time in over two decades.  The U.S. government people are theorizing that the Chinese government people are conspiring to take over the Philippines, or South Korea or D.C. or something.

In response to this illegal action attempted by the U.S. The Guardian reports that two former senators and ten taxpayers are suing the Philippine government people for violating their constitution.

Foreign military troops are banned from the Philippines unless a treaty is approved by 2/3 of the senate and ratified by the foreign state (in this case the U.S.).

So what is the real reason for the expanding U.S. military presence in the South China Sea?