New Delhi, Jan. 12 -- Iran is facing one of its gravest crises in years as protests that began over economic collapse have transformed into a nationwide political uprising. A deadly crackdown, an information blackout and threats of US military action have raised the stakes domestically and internationally. Here are the 10 key takeaways explaining what is happening and why it matters.

The protests began in late December after Iran's currency collapsed and inflation surged, sharply reducing purchasing power. Rising prices, subsidy cuts and unemployment triggered demonstrations by merchants, students and workers.

What started as economic outrage has evolved into a mass political movement. Protesters are now openly challenging Iran's cleric...