b. the arrest of a U.S. solider--referred to as the Tampico Affair
Unarmed sailors docked in a restricted Mexican port and were arrested and detained by the Mexican government. Wilson demanded an apology and salute. President of Mexico apologized but refused to salute and also accepted a shipment of weapons from Germany violating a Wilson embargo. This prompted a military response from the US which was responded with a quick retreat by Mexican forces.