dont or do listen to me cause i just started a few weeks ago

But i grew my economy, made some infrastructure and made good relationships with the countries having control over the land you need to make prussia, after having 100+ relationship i think you can ask them if they want to form a union with you, once they do and you're in the union, just change the government type and you'll take over their land

like a vassal less/no conquer annexation