I can add a bit of info. as to how this issue is handled under Aus Immigration law:
After 2 years as a Temporary Resident, a migrating Spouse must go through the whole process again...documents of proof of relationship etc etc etc before she/he is granted a Permanent Resident Status.
During the first 2 years, the Sponsor (in this case...me) is responsible for ALL costs associated with the migrating Spouse...health, education, support etc. Our Government does provide some free services along the way...language lessons, assimilation sessions and such.
If during this first 2 years, the relationship breaks down...for reasons NOT concerning physical or mental abuse, then the Migrating partner can opt to return home, or can seek to be granted a special Visa to enable them to stay here.
If there is any form of abuse contributing to the breakup, then it is a Police matter, subject to all the evidenciary rules and laws that protect ALL innocent parties...and punish the guilty ones.. Of course if the abuse is not reported, then nothing can be done.
But once the Australian Sponsor removes their sponsorship, the whole affair is in the hands of the Immigration Department who are normally very sympathetic for continuance of the Tempory Residence..
I believe this system discourages Marriages of Convenience (which it should !!) but at the same time allows a disadvantaged spouse the ability to make application to remain in Aus, despite the Sponsor removing their support.
Once the migrating partner has sucessfully received a permanent Resident visa, then all the rights of a Citizen are in play (except the right to vote, Join the armed forces or become a Politician !!!) At this time she/he cannot be forced out of the country, and on a relationship breakup, all Australian Divorce, custody and property Laws apply.
3 years after Permanent Residency, the Permanent migrant can apply for Citizenship.
I really feel that some of the Women who come here need a lot of protection from guys who do the wrong thing...but then again, some of the migrants should never have been let in in the first place...but that's another story !!!