Original: She emigrated from the UK to the US and created her own network television series, The Tracey Ullman Show, from 1987 until 1990, from which The Simpsons was spun off in 1989.
Simplified: She emigrated to the U.S. and ended up having her own network television series, The Tracey Ullman Show, from which The Simpsons was spun off in 1989.