Depends where in the western world. France and Italy... well obviously not now. But other countries, like the USA, Switzerland, Spain, Portugal (Franco and Salazar you see) are for varying reasons and in varying ways all more left wing than they were during the second half of the twentieth century.
Because it already raises the question of what "leftist" means in this contect - electoral success of left wing parties? of left wing social movements and/or trade unions? the attitude of the average person on the street? a leftwing economic order? or even just adopting left wing economic policies?
Generally talking for all the west, you can choice as weight the countries
all this are important but some are harder to know, so elections and government policies could be the right proxy
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I'm agree that we need to focus in the post WW2 era, in the 1929 and following years we have a large far right wave, in many european counytries
