"Boeing discounted the 737 MAX by more than 70% to force Bombardier to sell the C-Series below cost, which forced Bombardier to sell a controlling share to Airbus for $0."
I don't know any better, but I thought - statements by the companies to the contrary aside - that https://en.wikipedia.org/wiki/CSeries_dumping_petition_by_Bo... is what drove the Airbus partnership.