Community property laws consider husband and wife to be one in the eyes of the law and thus to own equally all the property earned by one or the other. This means that all income earned during marriage automatically belongs equally to both husband and wife. Only property acquired before marriage or received by gift or inheritance is outside of community property. The English law did not develop community property rules, and states based on English law do not provide for community property among husband and wife.
Community property is the law in southwestern and western states where there was an historic Spanish (Catholic) influence, including: Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, and Washington. The territory of Puerto Rico also developed community property laws. Wisconsin has recently adopted the community property laws unrelated to Spanish influence.
For most of the history of the United States, married couples in "community property" states enjoyed a federal tax benefit by being able to split their income 50/50 despite one spouse (usually the husband) earning most or all of the income. In 1946, the Republican Congress passed a nationwide federal tax benefit for the joint filing of tax returns, which allowed all married couples to attain the same tax benefit, including those married couples living in states that do not have community property laws.