The question is, who made the decision and when, to allow (or even facilitate) the movement of guns across the border into Mexico with no attempt or intent to intercept or even track their movement? And was the real intent for these weapons to be used in crimes in Mexico so that they could be traced by serial number through the BATFE to gun shops on the American side of the border? This for political gain with total disregard for the safety of the people of Mexico. I’m pretty sure that the latter angle represents and Act of War.
If the government of Canada (for instance) armed Al Qaeda operatives in the US we would consider it an act of war.