The equity portion of my portfolio is split 50/50 US/International and has been since before the the DOT.COM crash. The International portion is split into equal portions of Vanguard's European, Asian, and Emerging Market indexes because those were the only choices when I started, and I would not want to pay the capital gains needed to switch now.
I rebalance towards my target whenever I buy/sell equities. If my portfolio or the US market is hitting a new one year or longer high I allow myself to decrease my portfolio's overall equity percentage, but don't change the 50/50 US/International split. Likewise if hitting a new one year or longer low I allow myself to increase my portfolio's overall equity percentage. At the moment I'm 55% equities, 45% bonds with a rule that if the portfolio's equities drop below 51% or exceed 59% I must rebalance. Given this week's stock market highs I could lower the target percentage of equities right now if I wanted. That is my only "market timing."
Rebalancing means I was buying as Europe headed south, buying as Asia got "messy," and farther in the past was buying when Emerging was crashing. I've also sold when rebalancing.
International has lagged US for years at a time, but US has also lagged international for years at a time. The joy of diversification.