I wonder if the reason nothing is growing is because of the lack of direct sunlight. Regardless, you can buy a soil test kit at a garden center and test the soil pH, then modify the soil with lime to correct it.

Otherwise, modify the soil with compost or other organic material.

Even if that inexpensive soil test kit from the garden center is accurate it will not tell you why the soil is as it is and what you need to do to make that soil better. Contact your local office of the Cornell USDA Cooperative Extension Service and inquire about having a good, reliable soil test done. The most likely reason little is growing there is those pines blocked sunlight and the needles that fell every year also did the same so because any plants that might grow there, lacking sunlight, could not.
What you need to know about that soil is,
How much organic matter is in there?
How well does that soil drain and how well does that soil retain mositure?
What is the tilth (workability) of that soil?
What does that soil smell like?
What is the life (the wee critters) of that soil? How many earthworms do you find when working that soil?

Here is a link that might be useful: Cornell CES

I don't understand what has damaged the soil. Pines, by themselves, don't damage soil.

My guess would be that nothing's growing there now because there was too much shade and too much root competition from the pine trees. I don't see anything in your post about anything that would have poisoned or ruined the soil, like an oil spill or an old garbage dump or a gravel pit or old pavement.

You'll want to get the stumps and the larger roots out, but beyond that, maybe nothing. Get a soil test done to check the pH, nutrient levels, and organic content. If there's a lot of roots you can't get out then you might want to plant in raised beds.

It's possible the pines died of a soil-borne disease, which could affect any other trees you plant to replace them. 20 yr old pines should not be dying. There could also be drainage problems which would affect your future garden, as most pines don't like wet soil. The pines would be victims of the soil in these cases, not the perpetrators.

I agree with reg. The soil under a stand of conifers is generally rather poor fertility-wise but that's typically because of the root system of the larger, established trees hogging all the soil nutrients and available moisture from other, smaller plants with less aggressive root systems. Shade produced by the canopies and lack of rainfall getting through directly also will produce poor growth in many plants that one attempts to grow under these conditions. Lawns are notoriously tough to grow under these conditions and are generally not advised.

I doubt your soil is 'damaged' - just nutritionally poor. I agree with a soil test also, just to give you a baseline to move forward from, but incorporation of organic matter - compost - will be the most efficient way of improving soil quality in this area.

We live in the Adirondack Mountains and are surrounded by pines. We've reclaimed growing areas after pines were removed by using 'no dig' methods. That is building new soil on top of the barren ground. If you do a search for "no dig", "layered", or "lasagna" gardening you'll gather a wealth of information about it. Pretty easy compared to digging and tilling. And you can plant veggie transplants or flowers the same day, or wait.

Our soil tests neutral even though we use lots of pine needles as mulch and in compost. Pine needles as well as other organic material will initially create acidic conditions, but as organic matter decomposes the acidity becomes near neutral. A little lime takes care of the initial acid spike. Penn State College did a study on this. I didn't save the link to it, but it may pop up in a web search. Hope this helps.

The soil under the pine trees is not growing anything because they block all the light and suck up all the water. They have not done horrible things to the pand.

1 - shred and compost as much of the removed trees as possible.

2 - just layer that area with compost as in "lasagna garden" or "sheet composting" and plant.