Answer:
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.