Sentence:  With justified bitterness the author speaks of `` what seems to me to have been an inexcusable body of ignorance about the nature of the Russian Communist movement , about the history of its diplomacy , about what had <WSD>happened</WSD> in the purges , and about what had been going on in Poland and the Baltic States '' . 
Meaning of the word marked with <WSD> tags:  come to pass