How about climate change, the warming/drying in Europe which allowed for heavy cavalry to operate sussessfully starting not surprisingly at the driest place in

How about climate change, the warming/drying in Europe which allowed for heavy cavalry to operate sussessfully starting not surprisingly at the driest place in Europe at the time - in the Spain with Reconquista. Not surprisingly heavy cavalry quickly sunsets starting around Agincourt, beginning of the wet Little Ice Age, when heavy French couldn't operate in the rain soaked fields. About the same time of the last Crusade when heavy European knights couldn't dominate lighter forces anymore.