Although Australia federated in 1901, it didn't gain legislative independence until 1942 (with effect from 1939) via the Statute of Westminster Adoption Act. The Australian Constitution is, in fact, contained in a piece of British legislation, and the UK Parliament retained the right to legislate with regards to Australia. Australia didn't gain "final independence" until the Australia Act in 1986, which removed any possibilities of British legislation applying to Australia. In fact, there is some debate as to when Australia actually became independent. Although it was certainly not at federation in 1901. I don't know of any sources that indicate that Britain feared war as a consequence of Australian federation. Britain had previously enacted an Australasion Federal Council in 1885 (which included a number of the colonies and Fiji) to deal primarily with issues of trade and defence. It was a very slow and gradual process.