Although contemporaneous equity index returns are highly correlated I'm sure it's very difficult to say that one index leads another (at least in any consistently useful, tradable way). Buying (say) US indices in the US session may well trigger buying in other equity indices, but that trading is effectively instantaneous. Once you examine correlation of non-contemporaneous returns (ie does one asset lead another?) all those strong correlations more or less vanish.
Of course, I'd be delighted if anyone can show otherwise!
If one index consistently leads another that implies a free lunch. Is that plausible?
It's clear that indices see most movement in their local session and correlated (but smaller) moves are normally seen in foreign markets. On charts, this might suggest that (say) during the Asian session, Asian indices are 'leading' others, but I don't believe they are, at least not in any useful way. I think it's an illusion.