老师说下面一句中的 and because of that 也可换成 because of which，但要去掉 and：

Later in the next century, people from England made voyages to conquer other parts of the world and because of that, English began to be spoken in many other countries. 后来，在17世纪英国人开始航海征服了世界其他地区。因此，许多别的国家开始说英语了。

我不明白为什么 and because of that 变成 because of which，为什么要去掉 and？

句子来源：高中英语人教版必修一Unit 2（THE ROAD TO MODERN ENGLISH）