In an EU country elections are held for the national parliament. The winning party usually creates a coalition with another party to create a majority in parlia

In an EU country elections are held for the national parliament. The winning party usually creates a coalition with another party to create a majority in parliament. This gives them legislative powers. In a parliamentary system the legislature picks the prime minister (executive), therefore the coalition now controls the executive branch too. Now the executive branch appoints someone to the EU commission. The EU commission holds legislative power in the EU. EU parliamentary elections pick MEPs. The successful national parties are going to find now success in MEP elections, because they're already successful locally. This same national party is part of an EU-wide along with other similar parties from other EU nations. The elected MEPs will have EU-party affiliations based on that. Or in other words, it's the same groups of people in power on all of these levels.