The United Kingdom this week announced a sweeping set of boycott measures and sanctions aimed at Israel, the most aggressive measures ever taken by any non-Muslim country. Canada, France, and several other countries also vaguely pledged to pursue similar policies. This targeting comes after these countries’ attempt to “save” the “two-state solution” — the recognition of a Palestinian State — failed. The boycotts are not required by any principles of international law. But they will force American companies that comply with them to violate U.S. federal law.The boycotting governments invoke international law as justification, claiming the measures just apply to what...