Complex sentence: The defeat caused a rift between the Dutch and British governments, who now began to realise that they had overestimated the military capability of the Republic and, therefore, its ability to resist the French forces.
Split into simpler sentences: The defeat caused a rift between the Dutch and British governments. The British now began to realise that they had overestimated the military capability of the Dutch Republic and, therefore, its ability to resist the French forces.