Complex sentence: Because of the multi-party system of the Netherlands, no single political party (in the modern sense) has ever had a majority in parliament since 1900, the formation a coalition of two or often three parties is always necessary.
Split into simpler sentences: Because of the multi-party system of the Netherlands, no single political party (in the modern sense) has ever had a majority in parliament since 1900. A coalition of two or often three parties is always necessary.