While Convention forces occupied Mexico City, Carranza maintained control over two key Mexican states, Veracruz and Tamaulipas, where Mexico's two largest ports were located. Carranza was able to collect more revenue than Villa. In 1915, Villa was forced to abandon the capital after a number of incidents involving his troops. This helped pave the way for the return of Carranza and his followers.
To combat Villa, Carranza sent his ablest general Obregón north, who defeated Villa in a series of battles. Meeting at the Battle of Celaya in the Bajío, Villa and Obregón first fought from 6 to 15 April 1915, and Villa's army was defeated badly, suffering 4,000 killed and 6,000 captured. Obregón engaged Villa again at the Battle of Trinidad, which was fought between 29 April and 5 June 1915, where Villa suffered another huge loss. In October 1915, Villa crossed into Sonora, the main stronghold of Obregón and Carranza's armies, where he hoped to crush Carranza's regime. However, Carranza had reinforced Sonora, and Villa again was defeated badly. Rodolfo Fierro, a loyal officer and cruel hatchet man, was killed while Villa's army was crossing into Sonora.
In November 1915, Carranza's forces captured and executed Contreras, Pereyra, and son. Severianco Ceniceros also accepted amnesty from Carranza and turned on Villa as well. Although Villa's secretary Perez Rul also broke with Villa, he refused to become a supporter of Carranza.
After years of public and documented support for Villa's fight, the United States refused to allow more arms to be supplied to his army, and allowed Carranza's troops to be relocated over U.S. railroads. Woodrow Wilson believed that supporting Carranza was the best way to expedite establishment of a stable Mexican government. Villa felt betrayed by the Americans. He further was enraged by Obregón's use of searchlights, powered by American electricity, to help repel a Villista night attack on the border town of Agua Prieta, Sonora on 1 November 1915. In January 1916, a group of Villistas attacked a train on the Mexico North Western Railway, near Santa Isabel, Chihuahua, and killed a number of American employees of the American Smelting and Refining Company. The passengers included eighteen Americans, 15 of whom worked for American Smelting. There was only one survivor, who gave the details to the press. Villa admitted to ordering the attack, but denied that he had authorized the shedding of American blood.
Before the Villa-Carranza irregular forces had left to the mountains in 1915, there is no credible evidence that Villa cooperated with or accepted any help from the German government or agents. Villa was supplied arms from the U.S., employed international mercenaries and doctors including Americans, was portrayed as a hero in the U.S. media, made business arrangements with Hollywood, and did not object to the 1914 U.S. naval occupation of Veracruz. Villa's observation was that the occupation merely hurt Huerta. Villa opposed the armed participation of the United States in Mexico, but he did not act against the Veracruz occupation in order to maintain the connections in the U.S. that were necessary to buy American cartridges and other supplies. The German consul in Torreón made entreaties to Villa, offering him arms and money to occupy the port and oil fields of Tampico to enable German ships to dock there, but Villa rejected the offer.
There were documented contacts between Villa and the Germans after Villa's split with the Constitutionalists. This was principally in the person of Felix A. Sommerfeld (noted in Katz's book), who allegedly funneled $340,000 of German money to the Western Cartridge Company in 1915, to purchase ammunition. Sommerfeld had been Villa's representative in the United States since 1914 and had close contact with the German naval attaché in Washington Karl Boy-Ed, as well as other German agents in the United States including Franz von Rintelen and Horst von der Goltz. In May 1914, Sommerfeld formally entered the employ of Boy-Ed and the German secret service in the United States. However, Villa's actions were hardly that of a German catspaw; rather, it appeared that Villa resorted to German assistance only after other sources of money and arms were cut off.