And then they stagnated and collapsed.
Germany, America, England and Russia all came from harsh climates. Now they're most powerful nations.
India is a basket case.
There is something to having to deal with all four seasons.
Herodotus' purported quote of Cyrus the Great near the end of the Histories could be applied to the question.
Climate change is 100 percent natural 100 percent of the time, and true pandemics are also natural events. Roman fortunes sometimes rose and fell due to one or both.
The Roman Empire started with the conquest of Ostia (now called Ostia Antica) around or before (perhaps well before) 500 BC and ended in 1453 (a mere 39 years before Columbus' first big gig) with the fall of Constantinople.
It grew out of their response to attacks from hostile rivals in Italy, and the Gallic invasion of Italy, then the Carthaginians, but thrived and expanded due to systemization and ongoing reform of the Roman military model.
The use of a siege gun ended it, but 1900 years is not a bad run.
[snip] ...having got the king's consent by thus cunningly addressing him - chiefly, O Cyrus! come now, let us quit this land wherein we dwell - for it is a scant land and a rugged - and let us choose ourselves some other better country. Many such lie around us, some nearer, some further off: if we take one of these, men will admire us far more than they do now. Who that had the power would not so act? And when shall we have a fairer time than now, when we are lords of so many nations, and rule all Asia?" Then Cyrus, who did not greatly esteem the counsel, told them, - "they might do so, if they liked - but he warned them not to expect in that case to continue rulers, but to prepare for being ruled by others - soft countries gave birth to soft men - there was no region which produced very delightful fruits, and at the same time men of a warlike spirit." So the Persians departed with altered minds, confessing that Cyrus was wiser than they; and chose rather to dwell in a churlish land, and exercise lordship, than to cultivate plains, and be the slaves of others. [/snip] (Herodotus, The Histories, tr. by George Rawlinson