The growing aggressiveness of Russia towards its East European neighbors (especially ones that used to be part of Russia) has led these countries to revive military practices they thought they were done with. This includes civil defense and training citizens on how to resist and survive if again occupied by Russia.
Some of these nations, like Lithuania, are also reviving the militia. These were local groups of men who had military experience that were supplied with weapons and uniforms and training on how to resist an invasion. These “popular militias” were quite popular and widely used when much of East Europe (especially Poland and the Baltic States) got their independence after World War I ended (1918) only to lose it again when World War II began in 1939. The Russians noted that most of the local guerilla fighters in these countries, who continued fighting the Russians into the 1950s, were former militia members. So the militias were forbidden until the Russians left in 1991. There was some initial enthusiasm for reviving the militias after that but the enthusiasm waned through the 1990s. But now the militias are popular again and thousands of Lithuanians have already joined and more want to. While the militias will not stop an invasion that are one more thing for a potential invader (mainly Russia) to worry about and if nothing else it delays the Russians a bit more so that more NATO reinforcements can arrive. In the long-run NATO would be obliged to continue fighting and get the invader out. This is easier if the other NATO countries have seen that the locals are willing to die for their freedom and everyone remembers that Western allies failed to show up in 1939.