So reading through the 6th ed I thought the concept of allies was quite a new and exciting idea. When chaos daemons first came out I had something similar in mind while playing CSM but there wasn't anything "official", just homebrew rules. If you look at the chart on page 113 (at least that's what it is in my edition), I found two odd relationships. First, Eldar and Dark Eldar are considered battle brothers. Second, Space marine and tau are considered battle brothers. In regards to the eldar, from what I read, the eldar are not fond of their fallen brethren whatsoever. And for the space marines and tau, what happened to "Let not the alien live?". Maybe I'm missing something here but these seem like a couple odd pairings. Thoughts?