Space.com: Soyuz Spacecraft: Backbone of Russian Space Program

For years, the only method of delivering crew to the ISS was the Soyuz craft, leading NASA to purchase seats for their astronauts. According to Spaceflight Now, NASA bought 71 seats at a cost of nearly $4 billion over the course of six years. As of 2020, the SpaceX Dragon rockets can deliver American crew to the space station.