Where It All Goes Down
It's believed that "Italia mia" was composed around 1344 or 1345 in Parma, Italy, and we can see from line 6 that the speaker of the poem is sitting, "sad and grieving," near the Po River. Okay—we know that Parma is about 33 kilometers away from the Po River proper (thanks Google Maps). But the Parma River is a tributary, so we'll cut Petrarch some slack on this one.
Petrarch doesn't just give love to the specific place of his birth, though. He also mentions the Tiber and the Arno, rivers flowing through central Italy. By letting those other rivers into the poem to represent, Petrarch is stepping outside home boundaries to show how widespread the problem of warfare really is.
Petrarch has a serious thing for his native land. He talks about Italy as if it were his beloved (note that "lovely body" in line 3) or the Garden of Eden. His anger stems from the abuse of this gorgeous place at the hands of the nobility. They mismanage the "beautiful regions," flood the "sweet countryside" with mercenaries, and bathe the "verdant plains" with blood. They're "despoil[ing] the fairest part of all the world" for crying out loud.
Okay, you get the point: Italy's awesome. That seems like desperately little to say in 122 lines. But keep in mind that Petrarch's perspective in this poem is quite unique back in the day. He's detaching himself from the clannish loyalties that have caused so much trouble in the past so that he can love all of Italy at once. It's a big step for a guy from Tuscany to take. Thanks to his use of setting here, though, he's able to take it.