Complex sentence: The idea of an "Anzac Day" had been mooted since shortly after the Gallipoli landing in 1915-and there were a range of events in 1915 so-named-and it was in Queensland that the first major organisational endeavours towards an anniversary commemoration began.
Split into simpler sentences: The idea of an "Anzac Day" had been mooted since shortly after the Gallipoli landing in 1915 and there were a range of events in 1915 bearing that name. It was in Queensland that the first major organisational endeavours towards an anniversary commemoration began.