The Lambda Resistance, or commonly known as the Resistance was a loose, covert rebel network of oppressed peoples from multiple universes all united under the shared goal of defeating the Combine and restoring freedom to their worlds and universes.
Inspired, in part, by the Golmar Earth Freedom Fighters, the Lambda Resistances often cases the primary resistance groups against Axis rule, all characterized by their use of the Lambda symbol as a symbol of resistance and freedom against often cruel and brutal Axis dominance.
Since the formation of the Axis of Empires and Alliance of Nations, there have been numerous resistance groups fighting against the two factions, moreso the former than the latter, especially against the single most powerful memberstate of the Axis, the Empire of the Combine Race.
It's not unsurprising that by the end of First Multiverse War, the Lambda symbol is considered a symbol of resistance, of freedom, of opposition to totalitarianism, authoritarianism, and other forms of oppression all across the multiverse, all because of the GEFF influencing numerous resistance groups forged to fight against Axis rule and oppression.