The Posse Comitatus Act is the United States federal law (18 U.S.C. § 1385, original at 20 Stat. 152) that was passed on June 18, 1878, after the end of Reconstruction and was updated in 1981. Its intent (in concert with the Insurrection Act of 1807) was to limit the powers of Federal government in using federal military personnel to enforce the State laws.
The Bill/Act as modified in 1981 refers to the Armed Forces of the United States. It does not apply to the National Guard under state authority from acting in a law enforcement capacity within its home state or in an adjacent state if invited by that state's governor. The U.S. Coast Guard, which operates under the Department of Homeland Security, is also not covered by the Posse Comitatus Act, primarily because the Coast Guard has both a maritime law enforcement mission and a federal regulatory agency mission.
When you see the legislation that has been passed such as the repeal of the Posse Comitatus Act, it now allows the military to take over police duties. That was the 1878 Posse Comitatus Act following the Civil War. The military was everywhere (after that war until 1878).
So now the military can come back onto the streets. They know that unrest is bubbling over everywhere. Its happening in Romania, Slovenia, and around the world. The unemployment levels are hitting new highs. People are going into poverty and losing everything.
I hadnt realized Posse Comitatus had been repealed. On December 31, 2011, Obama signed the National Defense Authorization Act (NDAA) codifying indefinite military detention without charge or trial into law for the first time in American history. The ACLU has significant discussion of the ramifications.