The Trump administration has added six countries to its contentious list of states whose citizens are banned from obtaining certain types of visas to enter the United States. The list now includes Nigeria, Africa's most populous country and largest economy, along with Myanmar, Eritrea, Kyrgyzstan, Sudan and Tanzania. The travel ban already affected 135 million people worldwide, but in its new expanded form it has an outsized effect on Africa: fully a quarter of the continent's people (about 300 million people) are affected by the measures. The US says the travel ban is justified for security reasons. Here's a look at the restrictions, which vary from country to country.