After 1250. there was a substantial die-off of humans. Much of that was caused by Bubonic plague, but how much of that was caused by crop-failure-driven poor nutrition making Europeans susceptible to communicable disease is now hard to determine. The English used to make their own wine in the Medieval Warm period. Other less dramatic changes after the end of the Medieval Warm period. By the 1600s, Englishmen used to set up markets on the ice at London, because the Thames would freeze over solid, very solid, in fact.No, it wasn't. There are some who believe solar cycles have little to no influence on temperatures here on Earth. This seems to be a recent phenomenon as growing up I had always understood that solar cycles were a strong driver of past climate changes when humans could not have possibly made a difference since we weren't around for most of it.
I wish all of this was about the science and not the politics, because it is actually a fascinating subject. Our world is a small refuge in a vast and hostile universe. Understanding our climate and the factors that contribute to it is an important endeavor to our future. Our arrogance belies the fact that our understanding is in its infancy and that there is still much to be learned. 100 years from now people will (hopefully) chuckle and be amazed at our ignorance and arrogance much like we are at the science of 1915. Think of all the advancements made since then, from medicine to astrophysics to travel to nuclear physics to meteorology and climate sciences and so on...
I have read a bit about the American Civil War, and, while admittedly anecdotal, the ground in Virginia was covered with snow from December through February, and into March during the war. That rarely happens now. The last time that happened in Virginia was 2009, but before that it was quite a while. Something is causing that change.