To Major General Henry W. Halleck
Commanding The Department of Missouri

General;
As an insurrection exists in the State of Missouri, you are hereby authorized and empowered to suspend the Writ of Habeus Corpus within the limits of the military division under your command and to exersise martial law as you find it necessary in your discretion to secure the public safety and the authority of the United States.

In writing whereof, I have hereunto set my hand and caused the seal of the United States to be affixed at Washington, the second day of December 1861
Abraham Lincoln

Now according to Ex Parte Milligan;

Suspension of habeas corpus is unconstitutional when civilian courts are still operating; the Constitution provided for suspension of habeas corpus only if civilian courts are actually forced closed.

Does anyone agree that Lincoln broke the law here? There is one point I need to set here, this ruling came in 1866.

But Exparte Merryman dated 1861;
Ex parte Merryman, 17 F. Cas. 144 (1861), is a well-known U.S. federal court case which arose out of the American Civil War. Against President Abraham Lincoln's wishes, Chief Justice Roger Taney, sitting as a judge of the United States Circuit Court for the District of Maryland, ruled: "1. That the president [...] cannot suspend the privilege of the writ of habeas corpus, nor authorize a military officer to do it. 2. That a military officer has no right to arrest and detain a person not subject to the rules and articles of war [...] except in aid of the judicial authority, and subject to its control."

For those who hold Lincoln on high, he was a Military Dictator,,,,