Thousands of protesters demonstrated Friday across Yemen, some supporting the Shiite rebels who seized the capital and others demanding the country's south secede after the nation's president and Cabinet resigned. President Abed Rabbo Hadi, a U.S. ally in its campaign against Yemen's local al-Qaida branch, stepped down Thursday with his Cabinet over the pressures by Houthi rebels who demanded a bigger share of government power. A faction of southerners, who oppose the Shiite power grab and live in what was a separate country until 1990, have seized the opportunity to press their case for independence. In Sanaa, which Houthis seized...