Feeding more passengers to my airline sounds like a plus. I also don't remember any layoffs when we started a code share with either KLM or CAL. Refresh my memory on how those code shares worked out
On the CAL codeshare there were no layoffs but the KLM situation was very different.
While the pilot community came out of the deal relatively unscathed there were route losses for NWA which were partly due to the code-share and partly due to the change in strategic policy at the MSP HQ.
Around 10 years ago NWA decided to work on three core strengths - Its Pacific operation at Narita, the hubs at MSP, DTW and MEM and the partnership with KLM. As a result they downsized stations like Boston and Milwaukee which were then working as min-hubs. Transatlantic routes from BOS to GLA and BOS to LGW and I think BOS to CDG were all closed.
Passengers had to use the AMS hub and use KLM feeders to get to their European Destinations. In Europe the whole marketing operation was closed and handed over to KLM.
While short term the effect seemed to be a loss of routes for the red tails, the long term effect was major growth of the Amsterdam hub and consequent increase in NWA aircraft serving that hub.
Ten years ago before the partnership with KLM there were only two red tails a day in Amsterdam - a BOS and a DTW. Now there are around 11 with BOS, MSP (2), DTW (2), EWR, JFK, IAD, MIA, SEA and BOM.