Generally, in Washington State, the driver on the left must yield to the driver on the right.
However, there are exceptions and the details of your accident will determine in one person is 100% at fault or if there is some shared fault.
Often getting the advice of an attorney is critical and determining what options you have after such an accident.
If you are involved in an accident at an uncontrolled intersection you should contact an experienced WA injury attorney to see if you have a case. You can also order Car Accident Secrets Unlocked for free if you're Washington state resident. If you want help now, call 425-399-7000!