Complex sentence: Newcastle believed that the election of Joseph was sealed, but when he travelled to Vienna he found the Austrians were unwilling to proceed using the requirement that they be forced to pay a small payment of money to the Palatine as justification for their refusal.
Split into simpler sentences: Newcastle believed that the election of Joseph was sealed, but when he travelled to Vienna he found the Austrians were unwilling to proceed. Using the requirement that they be forced to pay a small payment of money to the Palatine as justification for their refusal.