How do I punctuate this sentence so it is grammatically correct?

There is an idea that has plagued America for almost a century; an idea which has lured many into a trap; one that has poisoned the minds of ambitious men and women regardless of their class, gender and ethnicity.

The problem is that it's too long. You need to break it up. Here's one way:

"There is an idea that has plagued America for almost a century, an idea which has lured many into a trap. It has poisoned the minds of ambitious men and women, regardless of their class, gender, or ethnicity."

Here's another way:

"There is an idea that has plagued America for almost a century. This is an idea which has lured many into a trap. It has poisoned the minds of ambitious men and women, regardless of their class, gender, or ethnicity."

I believe it's technically correct as it's written. It could be either condensed or split into multiple sentences for clarity, but sticking to your request to modify this sentence, I would say something like:

"There is an idea that has plagued America for almost a century, an idea that has lured many into a trap, poisoning the minds of ambitious men and women without regard to class or ethnicity."

I took out "gender" since you had already made a point to say "men and women". An alternative would be:

"There is an idea that has plagued America for almost a century, an idea that has lured many into a trap, poisoning ambitious minds without regard to class, gender, or ethnicity."

The other changes I made are just a matter of preference.

The first answer has no idea what he is talking about. I've had most of the college english. Semicolons are followed by a list. They don't belong in your sentence.

Try this: There is an idea that has plagued America for nearly a century, an idea that has lured many into a trap: a trap that has poisoned the minds of ambitious men and women regardless of their class, gender, or ethnicity.

No comma after women.

How many different ways do you think there are? hah well here is a good mixed option...

Why would you want to make this one sentence?

"There is an idea that has plagued America for almost a century, luring many into a trap; poisoning ambitious citizens minds regardless of their class, gender, or ethnicity."

Looks good to me as it is.