In the United States, the property included in a marriage can be categorized into marital property and community property. Marital property generally refers to all assets and debts acquired during the marriage, regardless of whose name they are in. This includes income earned by either spouse, property purchased with marital funds, and any inheritance or gifts received during the marriage. Community property, on the other hand, is a system that applies in certain states, where all property acquired during the marriage is considered jointly owned by both spouses. This system is prevalent in states like California, Arizona, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, and Wisconsin.

The rationale behind including marital property in a marriage stems from the principle of equitable distribution. According to the U.S. Supreme Court, marital property should be divided in a manner that is fair and equitable, considering factors such as the duration of the marriage, each spouse's contributions to the marriage, and each spouse's economic circumstances. This principle is enshrined in the Uniform Marriage and Divorce Act of 1970, which has been adopted by many states.

Data from the U.S. Census Bureau indicates that the average length of a marriage in the United States is approximately 12 years. During this time, both spouses contribute to the accumulation of marital property. For instance, a study by the National Center for Family & Marriage Research found that in 2019, the median net worth of married couples was $171,000, compared to $42,000 for single individuals. This highlights the importance of marital property in the financial well-being of married couples.

Moreover, the division of marital property is crucial in the event of a divorce. According to the American Bar Association, approximately 40 to 50 percent of marriages in the United States end in divorce. In such cases, the equitable distribution of marital property ensures that both parties are not unfairly disadvantaged. The U.S. Supreme Court has emphasized that the division of marital property should not be arbitrary but should take into account the specific circumstances of each case.

In conclusion, the inclusion of marital property in a marriage is essential for ensuring equitable distribution of assets and debts, as well as for the financial stability of married couples. The data from the U.S. Census Bureau and the American Bar Association underscores the significance of marital property in the context of American family law.