they say that in Africa government and law enforcement are weak and corrupt. So, does this mean that they would not have much ability to prevent people from migrating to another country, violating whatever visa regime they have there? Or are there strong extra-legal restrictions on migrants such as the locals violently attacking them?
Do you have a specific country in mind? “They say in Africa …” sounds a bit daft.
I know a little bit about South Africa because that is where I am from. In some sense it can be compared to the United States - illegal immigration is not a big problem between say South Africa and Botswana because both have a high quality of life for the region, much like the United States and Canada. Illegal immigration is a problem between South Africa and Zimbabwe, much like the United States and Mexico, because of a disparate quality of life and lack of opportunities in one country. Like the United States / Mexico border, the South African border is porous, long and difficult to patrol, meaning many border crosses make it through, although some are caught and sent back home.
Regrettably South Africa has experienced significant incidents of xenophobic violence against illegal immigrants due to heavy competition for employment and resources, so yes, that is potentially a disincentive (although given the complete collapse of the Zimbabwe economy I completely understand why someone would take the risk).
To have a significant illegal immigration problem you would typically have a disparity in wealth between the two nations, and I suspect a country’s wealth goes hand in hand with a less corrupt government (and the better enforcement of laws, immigration related and otherwise).
If you are talking about two poor countries that have corrupt and weak governments, along with corrupt and weak border enforcement, then it is easy to imagine less difficulty in crossing the border. On the other hand, given the two lousy economies, you’ve also eliminated a big reason why people cross borders.
A lot of African borders are quite porous, especially Central Africa and the Sahel. Also, transhumanance is a common mode of life which doesn’t really let borders limit it. Driver8’s laid out the SA situation pretty clearly - we get illegals, but a lot of those entered *legally *and then don’t leave when visas expire. Other than from Zim, it’s actually pretty hard to get into SA illegally (Namib/Kalahari on one side, Kruger Park on the other).
There’s been the publicised xenophobic violence, but lots of Nigerians and Somalians and Zimbabweans are here anyway, and form their own communities and aren’t affected. It’s mostly the very poorest immigrants, who share townships with the poorest natives, who get attacked.