The Mexican Frontier, 1821–1846 published by other historians. This work was supplemented by additional primary materials which he discovered in the archives that allowed him to delve further into certain areas. "The Mexican Frontier" examines the southwestern United States, specifically the areas now known as Arizona, California, New Mexico, and Texas, in the twenty-five years between Mexico's independence from Spain and the beginning of the Mexican–American War. This resulted in the transfer of control of the border areas to the United States. In the early days of the Republic of Mexico, these areas comprised its northern border, including the territories of Alta California and
History of Costa Rica Following the Mexican War of Independence (1810–1821), Costa Rica became part of the independent Mexican Empire in 1821. Subsequently, Costa Rica was part of the Federal Republic of Central America in 1823, before gaining full independence in 1838. Its economy struggled due to lack of connections with European suppliers. In 1856, Costa Rica resisted United States settlers from mounting a take-over of the government. After 1869, Costa Rica established a democratic government. After the Costa Rican Civil War in 1948, the government drafted a new constitution, guaranteeing universal suffrage and the dismantling of the military. Today, Costa Rica is a