California had a significant presence in the eastern theater of the Civil War, despite being over 2,500 miles away

Californians wanted to support the nation they had only recently joined at the outset of the Civil War. Californians soon had the means to contribute financially and militarily to the war. Edward Baker, a senator from Oregon, was sent to Philadelphia in September 1861 to raise money for and lead a brigade in the name of California. The 1st, 2nd, 3rd, and 5th California Infanteries made up the California Brigade, as it later came to be known.

California did manage to get some of their residents to physically represent their state in the Civil War. Californians who were of Eastern ancestry wanted to take part in the Civil War's eastern theater in the summer of 1862. The group proposed to create a company of Californians for Massachusetts and contacted Massachusetts Governor John Andrew. Governor Andrew agreed to the proposal on the understanding that Californians would pay for their own uniforms, tools, and travel expenses.

The troops consented, and the 100 cavalrymen from California, known as the "California 100," left for Massachusetts to join the 2nd Massachusetts Cavalry. Later, three additional Californian companies joined the California 100 to become the California Battalion. The California Battalion joined Phil Sheridan's Army of the Shenandoah in 1864 and took part in the largest cavalry charge of the Civil War at the Third Battle of Winchester as well as the Union counterattack at the Battle of Cedar Creek. The California Battalion was active throughout the Shenandoah Valley campaign.