Pretty sure all countries that participates at Worlds (both ICU & IASF) must have some sort of governing body. The governing body for each country choose how to give out the Worlds bids that they have been given from IASF. Some European countries have specific "Worlds bid competitions", and some just use their Nationals. For example in Sweden, the top 2 teams in IAG 5, IAG 6, IOC 5 and IOC 6 at Nationals gets a bid to IASF Worlds for the next season (our Nationals is in May).
One time, there was a Swedish junior team competing at a German competition and was awarded a bid to Worlds in small senior. They couldn't accept it because the Swedish Cheerleading Federation doesn't let any Swedish teams compete in club divisions.