I think it is also interesting to study the money men and women bring separately into their relationship and how that plays into relationship dynamics.
That's... not true at all.
The IRS tax forms even have an entire category for people who are married but maintain separate finances. It's called "married filing separate".
Now in some states there are laws that property acquired after marriage is shared, you can still maintain separate finances, and then it is up to a judge to figure it out in the case of divorce.
Also, you keep what you entered the marriage with. If you maintain separate finances, it's a lot easier to disentangle if you get divorced.
I have a friend who is on his second marriage, and his wife is also on her second. They maintain separate finances because they were both burned on a divorce, and they are very aware of what is common property and what is not. They could split up pretty much any time without a lawyer because they keep such good books.
Common Law States
Most states, except those listed as community property states below, use the "common law" system of property ownership. In these states, it's usually easy to tell which spouse owns what. If only your name is on the deed, registration document, or other title paper, it's yours. If you and your spouse both have your name on the title, you each own a half interest in the property unless the title document says otherwise. If an item doesn't have a title document, generally you own it if you paid for it or received it as a gift.
Community Property States
If you live in a community property state, the rules are more complicated. But in general:
spouses own equally almost all property either one acquires during the marriage, regardless of whose name the property is in
half of each spouse's income is owned by the other spouse during the marriage, and
debts incurred during marriage are generally debts of the couple.
In community property states, the following is separate property:
gifts given to one spouse
property either spouse owned before the marriage and kept separate during the marriage, and
inheritances.
The community property states are: Alaska (by agreement), Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, and Wisconsin. (In Alaska, spouses can sign an agreement making specific assets community property.)
And why would Wisconsin choose this, when it never had any connection to Spain?