Militia units made up 70% of the U.S. Army that fought the Mexican War in 1846 and 1847. During this first American war fought entirely on foreign soil, there was considerable friction between regular Army officers and militia volunteers, a friction that would reappear during subsequent wars. 'Regulars' were upset when militia officers outranked them and at times complained that the volunteer troops were sloppy and poorly disciplined.
But complaints about the militia's fighting abilities declined as they helped win critical battles. The Mexican War set a military pattern which the nation would follow for the next 100 years: the regular officers provided military know-how and leadership; citizen-soldiers provided the bulk of the fighting troops.
The Civil War
In terms of the percentage of the male population involved, the Civil War was by far the biggest war in U.S. history. It was also the bloodiest: more Americans died than in both World Wars combined.
When the war began in April, 1861 at Fort Sumter, both Northern and Southern militia units rushed to join the Army. Both sides thought the war would be short: in the North, the first volunteers were only enlisted for 90 days. After the war's first battle, at Bull Run, it became obvious that the war would be a long one. President Lincoln called for 400,000 volunteers to serve for three years. Many militia regiments returned home, recruited and reorganized, and returned as three-year volunteer regiments.
After most of the militia, both North and South, were on active duty, each side turned to conscription. The Civil War draft law was based on the legal obligation to serve in the militia, with quotas for each state.
Many of the most famous Civil War units, from the 20th Maine which saved the Union line at Gettysburg to Stonewall Jackson's famous brigade of "foot cavalry" were militia units. The largest percentage of Civil War battle streamers are carried by units of the Army National Guard.
Reconstruction and Industrialization
After the end of the Civil War, the South was under military occupation. Under Reconstruction, a state's right to organize its militia was suspended, to be returned only when that state had an acceptable Republican government. Many African-Americans joined the militia units formed by these governments. The end of Reconstruction in 1877 brought the militia back to white control, but black militia units survived in Alabama, North Carolina, Tennessee, Virginia, and five Northern states.
In all sections of the country, the late 19th century was a period of growth for the militia. Labor unrest in the industrializing Northeast and Midwest caused those states to examine their need for a military force. In many states large and elaborate armories, often built to resemble medieval castles, were constructed to house militia units.
It was also during this period that many states began to rename their militia "National Guard". The name was first adopted before the Civil War by New York State's militia in honor of the Marquis de Lafayette, hero of the American Revolution, who commanded the "Garde Nationale" in the early days of the French Revolution.
In 1898, after the U.S. battleship Maine blew up in the harbor of Havana, Cuba, the U.S. declared war on Spain (Cuba was a Spanish colony). Because it was decided that the President did not have the right to send the National Guard outside the United States, Guard units volunteered as individuals - but then reelected their officers and remained together.
National Guard units distinguished themselves in the Spanish-American War. The most famous unit of the war was a cavalry unit partly recruited from Texas, New Mexico and Arizona National Guardsmen, Teddy Roosevelt's "Rough Riders".
The real importance of the Spanish-American War was not, however, in Cuba: it was in making the United States a power in the Far East. The U.S. Navy took the Philippines from Spain with little trouble, but the Filipinos wanted independence, and the U.S. had to send troops to hold the islands.
Because most of the regular Army was in the Caribbean, three quarters of the first U.S. troops to fight in the Philippines were from the National Guard. They were the the first American troops to fight in Asia, and the first to fight a foreign enemy who used classic guerilla tactics - tactics which would again be employed against U.S. troops in Vietnam more than 60 years later.
Problems during the Spanish-American War demonstrated that if the U.S. was to be an international power, its military was in need of reform. Many politicians and Army officers wanted a much larger full-time Army, but the country had never had a large regular Army in peacetime and was unwilling to pay for it. Further, states-rights advocates in Congress defeated plans for a totally Federal reserve force in favor of reforming the militia, or National Guard.
In 1903, a piece of landmark legislation opened the way for increased modernization of, and Federal control over the National Guard. The law provided increased Federal funding, but in order to obtain it, National Guard units had to reach minimum strengths and be inspected by Regular Army officers. Guardsmen were required to attend 24 drills per year, and five days of annual training, for which they received pay for the first time.
Information Courtesy of the Army National Guard