As a result of this research, publications on Chicano history as a whole have exploded over the last fifty years. This research includes studies of the Spanish conquest of areas that became part of the United States, such as from Texas to California. Others have focused on the Mexican experience after Mexican independence in 1821 and up to the time the United States forced a war on Mexico and conquered its northern frontier—El Norte. The period following the American conquest of what became the American Southwest has also received attention. However, historians have tended to study the twentieth century more, including mass Mexican immigration to the United States during the first three decades of the century. The Great Depression years have likewise received attention, as has World War II, when thousands of Mexican Americans went to war in support of the United States. Finally, the post–World War II era, especially the 1950s, is also beginning to receive attention. Some pioneering studies on the Chicano Movement also appeared during the last two decades of the twentieth century. These include works by Juan Gómez-Quiñones, Gerald Rosen, Carlos Muñoz, Richard Santillán, Christine Marín, Ignacio García, Ernesto Chávez, and Marguerite Marín. Gómez-Quiñones wrote on the Chicano student movement, as did Carlos Muñoz with a focus on Los Angeles. Gerald Rosen examined the ideology of the movement. One of the best works in this early literature was Ignacio García’s history of La Raza Unida Party. Richard Santillán also focused on La Raza Unida Party. Ernesto Chávez and Marguerite Marín, like Muñoz, focused on Los Angeles as a key location by examining manifestations other than the student movement. Finally, Christine Marín wrote one of the first biographies of Corky Gonzales, a key movement leader in Denver.