Complex sentence: The divergence of opinions on this matter between Maurice and Van Oldenbarneveldt were the first signs that the two de-facto leaders of the Dutch Republic were beginning to drift apart, and this rivalry would eventually lead to the arrest and execution of Van Oldenbarneveldt in 1619.
Split into simpler sentences: The divergence of opinion on this matter between Maurice and Van Oldenbarneveldt were the first signs that the two "de facto" leaders of the Dutch Republic were beginning to drift apart. This rivalry would eventually lead to the arrest and execution of Van Oldenbarneveldt in 1619.