The article describes the international cooperation of local governments, which are a form of decentralization of democratic states. This cooperation developed massively after the Second World War. Today more than 200,000 local and regional communities participate in it, cooperating not only by direct contacts, but also through various types of organizations and networks. This is a new and growing phenomenon in the international environment. On selected examples of Polish local governments, it is shown how strong are the positive ties between members of territorial communities from different countries, built by this cooperation. Their strength and nature are shown by presenting the activities of selected Polish local governments during the extreme crisis, i.e. the war in Ukraine. Thus, it was presented how Polish local governments help the attacked Ukrainians and Ukraine.