Since the start of the year, when Dentons announced plans to merge with the Chinese firm Dacheng to form a 6,600-lawyer colossus, hardly a week has gone by without at least one announcement of a law firm combination.

During the first half of 2015, Altman Weil counted 48 combinations between legal shops, the highest half-year total since the Newtown Square, Pennsylvania-based consultancy began collecting such data in 2008.