Major Dundee (1965) on Netflix

In 1864 Major Amos Dundee leads his troops into Mexico after a group of renegade Apache Indians, led by Sierra Chariba. On a recent raid, they kidnapped some young boys and Dundee is committed to retrieving them. His own Union troops are supplemented by Confederate prisoners of war. Led by Lt. Benjamin Tyree - he and Dundee were once friends - he gives his word that he will follow Dundee's orders until Chariba is caught. Over the course of several months, Dundee and his men not only have to fight the Apaches but also French troops. As the mission continues, tensions rise between the Union and Confederate troops leading to a final confrontation with their foe.