Afghanistan has been the target of conquest over the centuries for two main reasons. Both of these reasons have to do with its geographic location. First, Afghanistan has been near to relatively powerful countries that have naturally wanted to expand their borders. Second, it has stood between powerful countries and things that they wanted. Both factors have led Afghanistan to suffer from invasions many times.
The first known invasion of Afghanistan was by the Persian Empire. Persia was a very powerful empire and powerful empires tend to want to expand. Because Afghanistan happened to be next to a powerful empire, it got invaded. A similar thing happened when Alexander the Great invaded. He had conquered the Persians and wanted to keep going. The next thing after Persia was Afghanistan and so Afghanistan got invaded. A similar thing happened when Timur (usually known as Tamerlane) invaded in the 1380s. He had created an empire in Central Asia and Afghanistan bordered that empire.
The second reason why Afghanistan has been invaded over the years is its position between Central Asia and the Indian subcontinent. It was this position that made it a focus of the “Great Game” of the 1800s. The Russian Empire was a major power in Central Asia. Great Britain controlled the Indian subcontinent. Afghanistan lies between those two areas. The Russians would have liked to gain control of the subcontinent, partly to get access to the Arabian Sea and the Indian Ocean. Britain wanted to keep control of the subcontinent since India was the most important part of its empire. These factors led to further invasions of Afghanistan.
Thus, Afghanistan has been a target of conquest largely because of its geographical location, not because of anything that is intrinsically valuable about the land or its resources.