With a drone strike last week, President Donald Trump authorized the killing of a prominent Iranian military figure–Qassem Soleimani– and also reopened a potentially explosive debate about when presidents can use their military power without approval from Congress.

The House of Representatives is slated to vote on, and pass, a resolution aimed at limiting the president’s power to engage militarily with Iran. It is not expected to pass the Senate.

READ MORE: WATCH LIVE: House to vote on restricting Trump’s actions against Iran

As that debate swirls, we thought it might be helpful to look at recent conflicts which were—or were not—authorized by Congress.

First, some important terms that you will likely hear more this week:

Article II powers – this is a reference to the president’s powers enumerated in Article II of the U.S. Constitution. Article II designates the president as the commander-in-chief of the U.S. military.

War powers resolution – this can be a broad term, referring to an act of Congress intended to grant, or more often limit, broad war powers of the president. But it also is a phrase used to describe the 1973 War Powers Act, which set Congressional guidelines for the president’s deployment of military force.

Authority to Use Military Force – this is a resolution passed by each house of Congress which grants a president specific powers to launch military action, often against a specific group or location.

Recent major hostilities and authorization or lack thereof:

Korean War. 1950 – 1953.
No Congressional authorization.
1.7 million U.S. troops deployed in theater.

Vietnam War. 1964 – 1974.
No Congressional authorization.
3.4 million U.S. troops deployed in theater.

Gulf War. 1991.
Authorization for Use of Military Force granted by Congress.
House 250-183. Senate 52-47.
500,000 U.S. troops sent to Persian Gulf.

War on Terror. 2001 – present.
Authorization for Use of Military Force granted by Congress.
House 420 – 1. Senate 98 – 0.
Initially included 775,000 troops sent to Afghanistan.

Iraq War. 2002.
Authorization for Use of Military Force granted by Congress.
House 296 – 133. Senate 77 – 23.
170,000 U.S. troops at peak deployment in Iraq.