Relations between the United States and Mexico in the first half of the 19th Century were fraught with discord. The second half of the century was little better as European powers sought to leverage Mexico's enmity with its northern neighbor for advantage in North America.

This, the second in a series on U.S. foreign relations with Mexico, looks at the tumultuous years between 1850 and 1920.

U.S. Backs Juarez

Following political instability after the U.S.-Mexican War, Mexico fell into a full-blown civil war in 1857.

Liberals under Benito Juarez battled conservatives following Felix Zuloaga. The U.S. officially backed Juarez in 1859, and the Mexican liberals were able to occupy Mexico City. They were not, however, able to pay off mounting debts to European nations. Abraham Lincoln's administration crafted a plan to help Mexico pay its loans, but the U.S. Congress did not approve it.

In the meantime, Great Britain, Spain, and France made plans to invade Mexico and force payment. Such would have blatantly violated the Monroe Doctrine, but the European powers knew the United States could do little about it as the country faced its own Civil War.

The European countries also realized that a broken United States would enable them to exert some renewed influence in North America. They played both sides off the middle, maintaining relations with the United States while hinting they might also support an independent Confederate States of America. Great Britain and Spain were moderate in their approaches, but France, in a new empire under Napoleon III, saw a chance to re-exert monarchical power in the Western Hemisphere.

Maximilian I

Mexican conservatives, seeing Napoleon III's plan as a way to defeat Juarez and the liberals, courted France's Second Empire. French forces invaded Mexico, pushed the liberals aside, and installed Maximilian Ferdinand of Austria as Maximilian I, Emperor of Mexico.

The U.S. could do little but try to maintain amicable relations with France. Lincoln and Secretary of State William Seward feared anything else might drive France to recognizing the Confederacy. For a moment, France had the upper hand.

France bet on the wrong side, however, and the United States won the Civil War in April 1865. Then, with the backing of Secretary of War Edwin M. Stanton, U.S. General-in-Chief Ulysses S. Grant sent Major General Phil Sheridan (who had earned a reputation for ferocity in the Shenandoah Valley in during the Civil War in 1864) with 50,000 troops to the Rio Grande border to intimidate France.

The maneuver worked, and Napoleon III pulled his backing from Maximilian. Mexican revolutionaries deposed and executed him in 1867.

Revolutionary Mexico And A Newly Powerful U.S.

During the Mexican presidency of Porfirio Diaz (1876-1911), the U.S. and Mexico had a period of relative peace. Diaz endeavored to keep a stable government and economy. As a result, the United States supported his government and invested heavily in Mexican businesses and resources.

Revolution again began in Mexico in 1910 when liberals, tired of Diaz's dictatorial policies and sensing the vulnerability of his age, broke into open rebellion. As with the Texas Revolution, the Mexican Revolution of 1910 is complex. Read more here.

During the Mexican Revolution of 1910, Mexico drew the wrath of a new United States. This one was not in the midst of settling its own domestic problems, but it was now a bona fide world power. It had defeated Spain in the brief but galvanizing Spanish-American War of 1898; reaffirmed the Monroe Doctrine with the (Theodore) Roosevelt Corollary to that document; begun professionalizing its military branches; embarked on the digging of the Panama Canal, and created a new, steel-clad and steam-powered navy that Roosevelt sent around the world on a muscle-flexing tour.

The U.S. under Wilson was not afraid to intervene in Mexico. U.S. dollars backed some 45% of Mexican business, and the United States wanted stability there. But it also learned that Germany was shipping arms into Mexico to support new leader Victoriano Huerta, who himself had overthrown Diaz's successor Ferdinand I. Madero during the revolution. President Woodrow Wilson landed American troops at Veracruz and Tampico to stop the shipments. After an altercation between local police and U.S. sailors, Wilson ordered the Navy to bombard Veracruz, and U.S. troops occupied the port for seven months.

U.S. Punitive Expedition

Wilson, furious with Mexico, said he would teach Mexico and other Latin American countries how to "elect good men."

When Mexican revolutionary Pancho Villa attempted to drag the U.S. further into the fray by attacking Columbus, New Mexico, in 1916, Wilson sent Brigadier General John J. "Blackjack" Pershing and some 5,000 U.S. Army troops on a "punitive expedition" to catch Villa. In 11 months, they never found Villa. As the United States was now in World War I, Wilson pulled out the expedition and sent Pershing to France as head of the American Expeditionary Force.

Zimmerman Telegram

U.S. entry into World War I, in fact, indirectly involved Mexico. In early 1917, British intelligence intercepted a telegram from German Foreign Minister Arthur Zimmerman to the Mexican government. Fearful that the U.S. was about to enter the war on the side of Great Britain and France due to Germany's resumption of unrestricted submarine warfare, Zimmerman tried to enlist Mexico's help. If Mexico would tie down U.S. troops in a diversionary war on the Rio Grande, the Germany -- after it won the war in Europe -- would help Mexico take back all the territory it lost to the U.S. in the Mexican War.

There was never any way Germany could have fulfilled that plan. Nevertheless, its revelation combined with other outrages, such as the sinking of the Lusitania in 1915, drove the U.S. to declare war on Germany.

The United States, Great Britain, and France won World War I, and the Mexican Revolution ultimately ran out of steam. A looming second world war, however, would begin to change relations between the U.S. and Mexico.