Commentator Mark Shields said more Americans have been killed by gunfire since 1968 than in all the wars in the nation’s history. Is that correct?

Politifact checked it out and confirmed:
“Since Shields’ comparison was otherwise accurate, with about 1.4 million firearm deaths to 1.2 million in war, we rated his claim True.”

 
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Data:
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
Total Deaths 1,384,171

We should note that these figures refer to all gun-fire related deaths — not just homicides, but also suicides and accidental deaths. In 2011, about one-quarter of firearm-related deaths were homicides, according to FBI and CDC data. Using total firearm-related deaths makes the case against guns more dramatic than just using homicides alone.

Here’s a summary of deaths by major conflict:

Revolutionary War 4,435
War of 1812 2,260
Mexican War 13,283
Civil War (Union and Confederate, estimated) 525,000
Spanish-American War 2,446
World War I 116,516
World War II 405,399
Korean War 36,574
Vietnam War 58,220
Persian Gulf War 383
Afghanistan War 2,175
Iraq War 4,486
Total 1,171,177