Actually, the Mexican Army has invaded the United States over 200 times between 1996—2005 (latest graphic I have from DHS).
Several of those times the Mexican Army engaged (i.e., shot at) Border Patrol Agents and local law enforcement. That is an act of war.
So, you may be correct we are not in a state of cease-fire, however, we are in a case of active engagement.
The Mexican Army is hired by the cartels to escort drug smugglers.
And people wonder why ordinary Mexicans are trying to get the hell out of that benighted country by any means necessary.
Maybe after November Congress will have the guts to take meaningful action on armed incursions like those you mention.