Mark Amezquita (defendant), a sergeant with the United States Air Force, and Roberta Archuleta (plaintiff) were divorced in New Mexico in 1990. They had three minor children. The divorce decree required that Mark pay Roberta $600 per month in child-support payments. Sometime later, Roberta moved to California with the three children. In 1999, Roberta registered the New Mexico decree in Sacramento, California. Roberta also obtained an order to show cause, because she was seeking to modify the support order. At the time, Mark was serving in San Pedro, California, and the pleadings were personally served upon him there. Although the pleadings were served upon Mark in California, New Mexico remained Mark's domicile. Mark responded to the order to show cause, arguing that he did not consent to the requested order. Mark then obtained a lawyer, and the lawyer filed an amended response on Mark's behalf. The amended response asserted that New Mexico was the only state with jurisdiction to modify the child-support order. The child-support issue crossed state lines, which meant that the Uniform Interstate Family Support Act (UIFSA) applied. The UIFSA was a federal law adopted by every state that determined which state had jurisdiction over a child-support order involving multiple states. The California trial court held that it had jurisdiction to modify the New Mexico support order and also had jurisdiction to enforce the modified order, because Roberta registered the order in California. Mark appealed.