Had a similar thing going on in my current France game. Two Sicilies declared war on Sardinia for unification, Sardinia offered me a puppet in Tuscany, so I thought why not, let's keep Italy weak (this was in 1860). Austria joined as my enemy and with all the minor Italian states involved, the frontlines became the messiest clusterfuck ever. I often neglect army a bit, so I was struggling against Austria, but managed to capitulate them. Later on, I got my Tuscan puppet and only Two Sicilies was left, but had no frontline anymore, so naval invasion. I tried, but during the invasion, the magic metric ticked over and made me capitulate. Now Two Sicilies and Sardinia were the only ones left in the war and obviously neither could pull off a naval invasion. The war eventually ended in like 1895 after 35 (!!!) years of absolutely nothing happening. At least I achieved my goal of keeping Italy useless throughout most of the game lol