I’d be interested if there are any museums which focus on Italian history from the Napoleonic era thru the Risorgimento to the post WW2 era. I see that Rome has a Risorgimento museum, wondering if there are any more of interest in Rome, Florence or Venice.
In Venice-Mestre there's a relatively new museum focusing on the 20th century. It's called "M9". I haven't managed to get there yet--it's hard to tear myself away from Venice--but it sounds interesting.
A little over a year ago I saw a small exhibition about the Holocaust in Italy set up in the Jewish ghetto area of Rome. I believe it was quite new at the time. I had the impression it wasn't just a temporary thing. It was called "L'Inferno Nazista", and it was in a building called "Casina dei Vallati".
Also in Rome is the Museo Storico della Liberazione di Roma. It covers the period of Nazo occupation and the liberation.
The Museo Storico delle Liberazione is fascinating and well worth seeing although a bit out of the way.
Museo di Roma which is located between Campo dei Fiori and Piazza Navona covers the Napoleonic era through the early 20th century very well. It has many fine paintings and I loved the film footage playing continuously that shows the 1920's and 1930's excavations of the forum and the tearing down of medieval buildings in front of St. Peter's. This museum is never crowded.