(Mauricio Lima | The New York Times) Martin Mpofu, center, a student from Zimbabwe in weak health, is helped by his brother Maneedi, right, and Hatim Redouani, from Morocco, as they cross from Ukraine into in Medyka, Poland, Feb. 28, 2022. Africans who had been living in Ukraine say they were stuck for days at crossings into neighboring European Union countries, held up by Ukrainian authorities who pushed them to the ends of long lines and even beat them, while letting Ukrainians through.