As soon as I saw this thread I grabbed my copy of Peter Perla's 'The Art of Wargaming' alas there is no reference to 'Leadership' that I could see. I thought that SL did chart a new course in this regard, I seem to have a hazy memory of an article somewhere, ("Fire and Movement" maybe) that held the SL model up as a paragon of innovation. I have no reference unfortunately, sorry Michael.
Among SL's and ASL's virtues, besides the whole 'System', were cited the Leadership factor on morale, as has been noted here, and modifying the firepower of units and hitting ability of guns. The other notable difference to other war games was the sheer amount of information on the counters.
I'm sure you'll agree that ASL packs more info on a counter than any other game prior to 1976-87.
Thanks for all the responses so far.
I don't know if ASL packs more info on a counter or not; certainly the rule book appears to be the longest rulebook of any tactical - or other kind - of wargame to that point in time. I've identified about 120 20th century tactical (man-to-man, squad and platoon based) games published from the start of the hobby in 1958-ish to 1999. (Anyone who thinks the hobby is dying can be heartened to know that the number of titles since 2000 is impressive, even if most of them are modules for ATS, Panzer Grenadier and ASL). I'm on my way to owning copies of all of them. Just doing a detailed examination of PanzerBlitz, which is what started it all in 1969 (and its predecessor, Tactical Game 3).
I think there were, however, many innovative concepts
as far as tactical games but I want to be sure that these weren't simply borrowed from other genres. Leadership is one of them. Ranged combat is another, ditto To Hit/To Kill process, concealment, etc.
PanzerBlitz does not seem all that innovative to be honest, looking back with 40 years of hindsight. The CRT seems very familiar - count up the odds, get a ratio, roll for 1 of a handful of possible results. That's not a criticism, but I think it highlights just how innovative Squad Leader truly was. Having said that, I don't have my copies of Grunt or Search & Destroy in hand yet, which were squad-based games which beat Squad Leader to the punch. Firefight was a good early effort, coming out a year before Squad Leader (some of you will remember it as a TSR re-release) and with a rule book about half as long.
The IFT itself seems very innovative, permitting the massing of fires, though perhaps it is six of one, half a dozen of another. It does give a player more options than someone in Firefight, say, who must fire each squad singly.
Rules for MGs, penetration, all that seems pretty groundbreaking as well.
But back on the topic of leadership - I think SL may have been the first to suggest that troops can do more than just be "suppressed" or "dispersed" but actually break down or even run away. One can argue this is factored into a "K" result in other games, but SL lets you rally them within the space of a 10 or 20 turn battle. Arguing how realistic that is might be like arguing the number of angels on the head of a pin, though.