Complex sentence: On 1 January 1901, Australia became a federation of six States, as the Commonwealth of Australia, which on 1 March 1901 took over the defence forces from the States, to form the Commonwealth Naval Forces.
Split into simpler sentences: On 1 January 1901, Australia became a federation of six States, as the Commonwealth of Australia, which took over the defence forces from the States. The Commonwealth formally took over the colonial navies on 1 March 1901, to form the Commonwealth Naval Forces.