I am an academic, originally from a country that requires a visa to enter to the US.
I don't have such a visa at the moment, which has been a hindrance in some cases where I was invited to visit some universities, and because of reasons I couldn't get a visa at the time.
So I would like to apply for a visa nowadays, so that when the next opportunity comes a-knockin', I will be able to say yes. But I worry that usually when applying for a visa you need some invitation or something like that.
Can I apply for a U.S. visa (whichever is suitable for academic visits) without an invitation? Or do I need to ask one of my colleagues to produce some invitation for this purpose?