It is written v'Asis, and we pronounce it v'Asisi!
Radak: You caused what I did to you
How will Hashem do like you did?
Rashi: He did to you evil, the payment for what you did.
Malbim: The first Bris that Hashem made with them when He took them out of Egypt was on condition that the guard His laws. They nullified it via transgressing the Bris. So Hashem will nullify this Bris from His side. The gift of Eretz Yisrael, the Beis ha'Mikdash and the kingdom were all contingent on this Bris. Their sins canceled it.
Why does it say "Bazis Alah Lehafer Bris"?
Rashi: You accepted [the Bris and curse] at Sinai - "Le'avrecha bi'Vris Hashem Elokecha uv'Alaso" (Devarim 29:11). Radak - "Lo Es Avoseinu Karas Hashem Es ha'Bris ha'Zos", "Lanu ul'Vaneinu Ad Olam La'asos Es Kol Divrei ha'Torah ha'Zos" (Devarim 5:3, 29:28).
