A more thorough explanation:

Martial law is a type of jurisdiction where military authority temporarily replaces civil authority. This happens when the government is unable to function due to war, natural disaster, or civil unrest. The military takes over the responsibilities of the branches of government that are unable to function, such as the legislature, executive branch, or the courts. Martial law is limited to times of emergency and must end when the emergency is over.

For example, martial law was declared in New Orleans, Louisiana by General Andrew Jackson during the War of 1812. It has also been declared by President Abraham Lincoln during the Civil War and by Governor Poindexter in Hawaii following the attacks on Pearl Harbor during World War II. In recent times, martial law has been declared in Ukraine and the Philippines.

In the United States, martial law can be declared on a national level by the President or Congress, or within the borders of a particular state by that state’s governor. Martial law has been declared nine times since World War II, most often in response to resistance of desegregation decrees during the Civil Rights era.

Martial law is different from military law, which only applies to individuals who are in military service. Citizens who are governed by martial law must still act in accordance with civil law. If citizens are wronged by the improper exercise of military power, they retain the right to seek remedies for that harm.

Overall, martial law is a temporary measure taken by the military to ensure the safety and security of citizens during times of emergency.