Keynesians believe that if government spends more, it creates wealth in the process because it is "creating demand." But only wealth generation can create demand for goods.
Most economists see GDP as a snapshot of the performance of the economy. However, it is better understood as a misleading statistic which fails to accurately describe what really is happening economically.
Neither the Ukraine war nor tough weather changes would threaten a global food shortage in a normal market environment. Unfortunately, world markets are riddled with regulations, killing production.
The scale of the sanctions which Washington has imposed on Russia (and Russians) should not distract us from a crucial fact. What Washington is doing against Moscow is not rare. It is something that happens every day.
It's unlikely that Putin had no idea of the immense costs that he and Russia as a whole would incur in undertaking this war, so he likely believed the alternative would have been even more costly.