Complex sentence: Australians for Constitutional Monarchy was active in challenging Australia's republican organisations and playing a key role in the "No Republic" campaign during the lead up to Australia's 1999 republic referendum, receiving 83.95% of the constitutional monarchist vote for the 1998 Constitutional Convention.
Split into simpler sentences: Australians for Constitutional Monarchy was active in challenging Australia's republican organisations in the lead-up to the 1999 referendum. The ACM played the key role in the "No Republic" campaign during the lead up to Australia's 1999 republic referendum, receiving 83.95% of the constitutional monarchist vote for the 1998 Constitutional Convention.