Most of the significant changes in the affordable care act went into effect on what date?

Most of the significant changes to the ACA went into effect on March 23, 2010.

Details:
The ACA was signed into law on March 23, 2010, by President Obama.
The major or significant changes that went into effect were
1. Grandfathered health plans:
This enabled people with existing health plans to keep their plans, provided that the insurer continued to offer the plan.
2. Non-grand fathered health plans:
Those who purchased health insurance plans after March 23, 2010, would eventually have to conform to the standards established by the ACA.

Note:
Many more changes were scheduled to go into effect after March 23, 2010.

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