According to Politifact who examined the claim by Mark Shields:
You know, Judy, the reality is -- and it's a terrible reality -- since Robert Kennedy died in the Ambassador Hotel on June 4, 1968, more Americans have died from gunfire than died in … all the wars of this country's history, from the Revolutionary through the Civil War, World War I, World War II, in those 43 years.
For the number of casulaties of war they cite a study of war-related deaths published by the Congressional Research Service, according to it, the number of casualties in wars and conflicts, up to Dec 22nd, 2014 was:
- Revolutionary War: 4,435
- War of 1812: 2,260
- Mexican war: 13,283
- Civil War (union and confederate)1: 525,000
- Spanish-American War: 2,446
- WWI: 116,516
- WWII: 405,399
- Korean War: 36,574
- Vietnam Conflict: 58,220
- Persian Gulf War (1990-1991): 383
- Worldwide U.S. Active Duty Military Deaths in Selected Military Operations
(1980-1996) (excluding Persian Gulf War): 362
- Operation Enduring Freedom (Afghanistan): 2,352
- Operation Iraqi Freedom (Iraq): 4,412
- Operation New Dawn (Iraq): 66
- Operation Inherent Resolve (military intervention against ISIS): 3
The report doesn't have one handy number or a quotable sum, all the numbers are in different tables
The numbers include all deaths, including non hostile deaths.
According to icasualties.org updated number for 2016 are 4,512 in Iraq and 2,392 in Afghanistan.
Summing all the numbers (using the 2016 numbers for Iraq and Afghanistan) gives a total of 1,171,785 dead.
As to the number of gunfire deaths:
The number of deaths from gunfire is a bit more complicated to total. Two Internet-accessible data sets from the Centers for Disease Control and Prevention allow us to pin down the number of deaths from 1981 to 1998 and from 1999 to 2010. We’ve added FBI figures for 2011, and we offer a number for 1968 to 1980 using a conservative estimate of data we found in a graph in this 1994 paper published by the CDC.
Here is a summary. The figures below refer to total deaths caused by firearms:
- 1968 to 1980: 377,000
- 1981 to 1998: 620,525
- 1999 to 2010: 364,483
- 2011: 32,163
A total of less than 1.18 million war casualties up to 2016, and more than 1.38 million death from gunfire between 1968 and 2011, which is considerably more.
1 - The report has a number for only union forces at 364,511, the number 525,000 for all deaths is given by politico.