Simplify the following text for a Grade 5 native English-speaking person.
Original: The club was founded in 1948 , three years after borders of Poland had switched westwards and the city of Zabrze ( until then called Hindenburg ) became part of the Polish Republic .
Simplified: GÃ rnik Zabrze is one of the most successful Polish football clubs , based in Zabrze , Poland . They started in 1948 .