The three Belarusian companies sell up to one-fifth of the world’s supply of potash, a fertilizer ingredient crucial to global food security. The United States removed sanctions both on those companies — Belaruskali, Belarusian Potash Company and Agrorozkvit — and on the state investment bank. All are pillars of the Belarusian economy, and the lifting of sanctions hands the country an economic lifeline.