What are some similarities between the governments of the United States and Australia?
The major similarity between these two governments is that both of them are constitutional federal democracies. In addition, both have some degree of separation of powers.
Both countries have written constitutions that are the supreme law of the land. In both cases, the constitutions give some powers to the states that cannot be taken away by the federal government unless the constitution is amended. Both countries' laws are made by elected legislatures that have two houses. In both countries, laws made by the elected legislatures may be overturned by courts if the laws are found to be unconstitutional.
Thus, the two countries have very similar systems. There are major differences, but they are less important than the fact that both countries are constitutional federal democracies.