After the overthrow of the government of Urbano Rattazzi, because of the popular indignation at the events in Aspromonte, the new prime minister Luigi Carlo Farini encouraged Nullo to form a legion of volunteers to intervene on the side of Polish insurgents against Russian domination, ensuring his lobbying at King Vittorio Emanuele II, to declare war on the Russian Empire. Nullo, already friends with Poles such as Ludwik Mierosławski and Marian Langiewicz, who supported him and Garibaldi in their past fights, quickly took to the Polish cause, soon organizing meetings in Bergamo and recruiting volunteers for the Polish cause, recalling Polish support for the Italian cause during the Napoleonic wars (Polish Legions in Italy), and even more so, during the Spring of Nations (Mickiewicz's Legion).