The EU isn't doing any direct fighting in the Russian-Ukranian war, we are however donating and selling things, and being a refuge for those who quite understandably fled in fear of their lives.
Nobody's actually violated our sovreignty yet, we have no casus belli to go to war. But as the phrase the bullet cartridge is named after goes: Si vis pacem, para bellum.
Or who is "we"?