We get our first clue to the specific problem in Petrarch's poem around line 20, when he throws this line out: "what are the swords of strangers doing here?" Now, Petrarch is not concerned about a display of foreign combat gear in a museum. He's using synecdoche to create a shorthand image for the German mercenaries who have been hired by the Italian nobility to fight with rival houses.
While the swords only get mentioned in line 20, the fallout from them is spread throughout the poem. In the opening lines, we see Italy's "mortal wounds" and in lines 21-22, Petrarch shows us the "verdant plain" as it is "painted red with that barbaric blood." It's really kind of gross. But Petrarch isn't going to mince words if he has a chance to stop the insanity.