The best option to complete the diagram comparing Texas and California is "Formerly part of Mexico."
Texas was annexed by the United States in 1845, and before that, it was an independent republic and part of Mexico. California was ceded to the United States in 1848 after the Mexican-American War, thus both states share the characteristic of having been part of Mexico before becoming U.S. states.
Other options do not effectively compare both Texas and California in the context provided.