"No Cross, No Crown" was a treatise written by William Penn in 1682.
As a sort of history joke, "No Cross No Crown" is a guideline that we on the Althistory Wiki inherited from our Internet grandparent, the CONLANG List (firstname.lastname@example.org) and our Internet parent, the Conculture Group (groups.yahoo.com/group/conculture/). Generally, it means that discussions of religion ("Crosses") and politics ("Crowns") ought to be avoided, or at least approached with caution.
"NCNC" has been summarized thus:
- "...no discussing actual religion / politics as issues per se (because of their high potential for causing heated Off Topic arguments)... whereas merely discussing *fictional* Crosses|Crowns, or the conlanging aspects of incidentally Cross|Crown themed content, is (ha) kosher." (from Conlang)
- "Basically, there will come a point when we have to discuss real world politics or religion in order to craft a more realistic secondary world -- but such discussions should *never* involve attitudes of religious or political superiority, intolerance, etc." (from Conculture)
Adapted to alternate history, the rule can be summed up like this: discussions on religion and politics should center on our fictional timelines and not devolve into debates on politics and religion in real life (OTL). It's a blurry distinction, definitely not a precise one, and as we talk about other timelines, some discussions on controversial topics in OTL are inevitable. That's why it's a general rule of thumb or a guideline, not an ironclad law.
No Cross No Crown mostly applies to our discussion, but the spirit of the rule can be extended to the actual writing of alternate history. Timelines that clearly show a bias or push an agenda are, simply put, bad AH, and for most of them are far less enjoyable to read than timelines that approach history, culture, religion and politics objectively. One of our guidelines for featured timelines is that they be neutral.
Finally, it's important to note that No Cross No Crown is a behavior standard that, like everything else, reflects the history and culture of the people that abide by it. Other online alternate history sites have different attitudes toward Crowns and Crosses in discussion; for this reason Counter-Factual.net was said to be more right-wing, for example, while AlternateHistory.com has a reputation for being more left-wing. In fact, both sites have entire sub-forums for OTL political debates.