Complex sentence: The game sold almost 50,000 copies in its first week in Japan and 1.44 million copies in the United States by December 2007, making it one of the best-selling GameCube games.
Split into simpler sentences: The game sold almost 50,000 copies in its first week in Japan. It sold 1.44 million copies in the United States by December 2007, making it one of the best-selling GameCube games.