Here's what Wikipedia has to say on Martial Law.
Martial law is the imposition of military rule by military authorities over designated regions on an emergency basis.
Martial law is usually imposed on a temporary basis when the civilian government or civilian authorities fail to function effectively (e.g., maintain order and security, or provide essential services), when there are extensive riots and protests, or when the disobedience of the law becomes widespread.
In most cases, military forces are deployed to subdue the crowds, to secure government buildings and key or sensitive locations, and to maintain order.[1] Generally, military personnel replace civil authorities and perform some or all of their functions. In full-scale martial law, the highest-ranking military officer would take over, or be installed, as the military governor or as head of the government, thus removing all power from the previous executive, legislative, and judicial branches of government.[1]
Martial law can be used by governments to enforce their rule over the public. Such incidents may occur after a coup d'