Louisiana State University's statistical summary of major American wars

I. The Military Participation Ratio

Conflict                   Population   Enrolled    Ratio
                           (millions)  (thousands)
Revolutionary War                 3.5    200.0      5.7%
War of 1812                       7.6    286.0      3.8%
Mexican War                      21.1     78.7      0.4%
Civil War: Union                 26.2  2,803.3     10.7%
         : Confederate            8.1  1,064.2     13.1%
         : Combined              34.3  3,867.5     11.1%
Spanish-American War             74.6    306.8      0.4%
World War I                     102.8  4,743.8      4.6%
World War II                    133.5 16,353.7     12.2%
Korean War                      151.7  5,764.1      3.8%
Vietnam War                     204.9  8,744.0      4.3%
Gulf War                        260.0  2,750.0      1.1%

The military participation ratio is the percentage of people under arms. While the ratio for the Second World War seems surprisingly high compared with those for the Revolutionary War and the Civil War, this is due to the fact that the War for Independence took place before the Industrial Revolution, and the Civil War occurred before its fullest impact, while the nation's womanpower was not tapped in either earlier conflict as well, for either military or economic mobilization. The figure "Enrolled" represents the number of personnel maintained in the service. It is somewhat unreliable, since it includes multiple enlistments in the case of wars prior to 1900, and is a gross figure, including all personnel ever in the service during the conflict. In addition, figures for post-1945 wars are polluted to some extent by the fact that a significant portion of the forces under arms during these conflicts were not actually directly engaged in the war, but were securing the nation's other global commitments.

II. Casualties

                                    <------------Casualties------------>
                                    [-----Deaths---]                             <-----Percentages-----> Duration 
Conflict                Enrolled    Combat   Other   Wounded     Total    Ratio  KIA    Dead   Casualty   Months  KIA/Month          
Revolutionary War          200.0    4,435   *          6,188      10,623   2.4   2.2%    2.2%     5.3%      80       55
War of 1812                286.0    2,260   *          4,505       6,765   3.0   0.8%    0.8%     2.4%      30       75
Mexican War                 78.7    1,733   11,550     4,152      17,435   1.3   2.2%   16.9%    22.2%      20       87
Civil War: Union         2,803.3  110,070  249,458   275,175     634,703   1.8   3.9%   12.8%    22.6%      48    2,293
           Confederate   1,064.2   74,524  124,000   137,000 +   335,524   1.7   7.0%   18.7%    31.5%      48    1,553
           Combined      3,867.5  184,594  373,458   412,175 +   970,227   1.7   4.8%   14.4%    25.1%      48    3,846
Spanish-American War       306.8      385    2,061     1,662       4,108   1.7   0.1%    0.8%     1.3%       4       96 &
World War I              4,743.8   53,513   63,195   204,002     320,710   2.7   1.1%    2.5%     6.8%      19    2,816
World War II            16,353.7  292,131  115,185   670,846   1,078,162   2.6   1.8%    2.5%     6.6%      44    6,639
Korean War               5,764.1   33,651   *        103,284     136,935   4.1   0.6%    0.6%     2.4%      37      909
Vietnam War              8,744.0   47,369   10,799   153,303     211,471   3.6   0.5%    0.7%     2.4%      90      526
Gulf War                 2,750.0      148      145       467 ^       760   2.6   0.0%    0.0%     0.0%       1      148

Combat deaths refers to troops killed in action or dead of wounds. Other includes deaths from disease, privation, and accidents, and includes losses among prisoners of war. Wounded excludes those who died of their wounds, who are included under Combat Deaths. Ratio is the proportion of wounded in action to combat deaths. Note that the wounded figures do not include cases of disease. Under Percentages, KIA refers to the percent of those enrolled killed in action, Dead to the percent dead from all causes, and Casualty to the percent killed or injured. KIA/Month, killed in action per month, gives a fair indication of the intensity of combat

Notes:
* Non-battle deaths not known for these wars.
+ Confederate non-battle deaths and wounded estimated.
& Actually only six weeks of sustained combat.
^ There was only one month of combat.

III. Financial Cost

Conflict                            Cost in $ Billions  Per Capita 
                                    Current      1990s  (in $1990)  
The Revolution (1775-1783)             .10         1.2  $   342.86
War of 1812 (1812-1815)                .09         0.7       92.11
Mexican War (1846-1848)                .07         1.1       52.13
Civil War (1861-1865): Union          3.20        27.3    1,041.98
                     : Confederate    2.00        17.1    2,111.11
                     : Combined       5.20        44.4    1,294.46
Spanish American War (1898)            .40         6.3       84.45
World War I (1917-1918)              26.00       196.5    1,911.47
World War II (1941-1945)            288.00     2,091.3   15,655.17
Korea (1950-1953)                    54.00       263.9    1,739.62
Vietnam (1964-1972)                 111.00       346.7    1,692.04
Gulf War (1990-1991)                 61.00        61.1      235.00

The table compares the cost of America's principal wars since 1775 on the basis of then current and 1990s dollars. Current dollars are the actual numbers spent at the time. Thus, a 1775-1783 dollar had the equivalent purchasing power of $10.75 in 1990s terms. Actually this conversion is only a very rough guide, but at least gives some idea of the relative costs of the ten wars on an adjusted basis. However, it is not possible to take into account drastic changes in social structure (most Americans were farmers in 1775, and didn't use much money), and the increasing affluence of American society over the two centuries covered by the table.
Note that the figures are for direct costs only, omitting pension costs, which tended to triple the ultimate outlays. The table also omits the cost of damage to the national infrastructure during those wars waged on American soil. Confederate figures are estimated.
For the Gulf War it is worth noting that various members of the allied coalition reimbursed the U.S. for 88-percent ($54 billion) of the amount shown, so the actual cost to the taxpayer was only about $7 billion, roughly the same as for the Spanish-American War, and on a per capita basis only $26.92, arguably the least expensive war in the nation's history.

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Sources: Table 2-23: "Principal Wars in which the US Participated: US Military Personnel Serving and Casualties" prepared by Washington Headquarters Services, Directorate for Information Operations and Reports. US Department of Defense Records.