This is a jukugo word that uses the on'yomi readings of the kanji. You haven't learned this reading for 幕 yet, so here's a mnemonic to help you:
If you try to peek through the bakufu's curtain you'll only see someone's back (ばく). They all huddle together to discuss things so a row of hunched backs is all you'll get out of the shogunate. That's not helpful.
The bakufu slaughtered my family.