Which Roman civil war brought Julius Caesar to Egypt during Cleopatra's struggle with Ptolemy XIII?

The Roman civil war that brought Julius Caesar to Egypt during Cleopatra’s struggle with Ptolemy XIII was Caesar’s Civil War. Caesar was pursuing his defeated rival Pompey when events in Egypt drew him into the Ptolemaic succession dispute.

After Pompey was assassinated in Egypt in 48 BC, Caesar arrived in Alexandria. Cleopatra VII and her younger brother Ptolemy XIII were nominal co-rulers, but their relationship had collapsed into armed conflict. Caesar intervened as an arbitrator, while also demanding repayment of debts owed by their father, Ptolemy XII.

The fighting in Alexandria is often called the Alexandrian War or Alexandrian phase of Caesar’s Civil War. Those names describe the Egyptian theater of the larger Roman conflict, so “Caesar’s Civil War” is the broad canonical answer. Caesar’s victory eventually restored Cleopatra to power alongside Ptolemy XIV.