I find it interesting how the warm years in the rest of the world seem to correspond to cold years in europe. The strange deep cold of early WW2 in Europe is also interesting.
This is quite a well-studied period that was probably linked to a large El Niño event - the climate cycle associated with shifting pressure patterns and a weakening of the trade winds in the Pacific.
The world warmed, apart from Europe which had a deep cold spell. And it probably had an impact on the outcome of WWII. The harsh winters at the time frustrated Hitler's armies as they invaded the Soviet Union.