As Members of Congress debate a massive health-care overhaul, they must deal with elements of the nation's health care system that date to World War II.

Some, such as a prescription drug benefit, were created deliberately. Others, such as Medicare and Medicaid, grew over the years.

And others, such as the system of private health insurance, came about almost by accident.

Below, we list seven key decisions that led to the development of the U.S. health care system as it is today and how they are affecting the debate.

1940s: Health Insurance Becomes a Benefit

Federal wage limits during World War II led U.S. businesses to begin offering health insurance as a benefit to attract workers.

WHY IT MATTERS: Today, 158 million Americans are insured through their employers, roughly 60 percent of non-elderly adults. But the link between your job and your insurance leaves the self-employed and the unemployed in more difficult positions.

1954: Employer-Based Health Care Goes Mainstream

The Revenue Act (Public Law 83-591) excluded business contributions to employee's health plans from federal income tax. This cemented the trend toward employer-based health coverage.

WHY IT MATTERS: The bill in the Senate is designed to leave this system in place, though critics contend that proposals such as a public option for government-run insurance plan would eventually undermine employer-based coverage.

1959: Congress Gets Its Own Plan

The Federal Employee Health Benefits Act (PL 86-382) provided coverage to federal workers and their families. Today, it is the largest employer-sponsored group health insurance program in the world, covering more than 8 million people, including Members of Congress.

WHY IT MATTERS: One compromise under discussion would eliminate the public option from the bill in favor of a national insurance plan similar to the Federal Employee Health Benefits Plan.

1965: The Poor and the Elderly Are Covered

The Social Security Amendments Act (PL 89-97) created Medicare, a health insurance program for seniors aged 65 or older, and Medicaid, a federal-state partnership to insure low-income pregnant women and children, disabled Americans and the elderly. Today, Medicare covers 45 million Americans ; Medicaid, 59 million.

WHY IT MATTERS: The aging population of Baby Boomers has strained the Medicare system. The health care proposal includes cost controls, though critics of the bill have said it will lead to cuts in benefits from the popular program.

1986: Laid-Off Workers Get Short-Term Help

The Consolidated Omnibus Budget Reconciliation Act (PL 99-272), or COBRA, requires employers to continue existing group health coverage for laid-off employees for 18 months. It also allows spouses and dependents to avoid losing coverage because of death or divorce.

WHY IT MATTERS: As a short-term fix, the health care overhaul would extend COBRA benefits until a new national insurance exchange is set up in 2013 or 2014.

1996: Pre-Existing Conditions are Partially Restricted

The Health Insurance Portability and Accountability Act (PL 104-193), or HIPAA, protected health insurance benefits for workers changing jobs. It also partially restricted insurance companies' use of pre-existing conditions to deny coverage.

WHY IT MATTERS: Just as this bill targeted the use of pre-existing conditions, the current proposal would end rescission -- the cancellation of policies because consumers made honest mistakes when filling out their medical histories.

2003: Medicare Adds Drug Coverage

The Medicare Drug, Improvement, and Modernization Act (PL 108-173) created the popular Medicare Part D prescription drug benefit. However, a coverage gap between initial benefits and total yearly benefits, known as the "doughnut hole," causes problems for some recipients.

WHY IT MATTERS: The health care overhaul would eventually close the doughnut hole by providing additional drug coverage over several years.

Sources: Kaiser Family Foundation, U.S. Department of Health and Human Services, CQ Weekly, CQ Almanac, and "Health Care Policy and Politics A to Z" by Julie Rovner.