Final answer:
Employer-based health insurance was triggered by World War II wage freezes, which led employers to offer health insurance as a fringe benefit to attract workers, and was bolstered by union-management negotiations.
Step-by-step explanation:
Employer-based health insurance as a benefit was primarily triggered by wage freezes during World War II. During this period, the U.S. government implemented wage controls to prevent inflation, which limited employers' ability to compete for workers through increased wages. As a result, to attract and retain workers, employers began to offer health insurance as a fringe benefit. This practice became increasingly popular because it did not violate wage controls, and health insurance benefits were not taxed as income, making them even more attractive to employees.
Union-management negotiations also played a role in solidifying the trend of offering health insurance. Unions, whose memberships and influence grew during the war, often negotiated for better benefits for their members, including health insurance. Once established, these benefits set a precedent that other employers followed in the competitive job market.