There is no right answer. Answers tend to fluctuate between 45% international to 0%. The 45% comes from the fact that currently about 55% of the world stock market capitalization is US. You'll have to do some reading and research and determine your own believes, values and judgment in this matter. If you cannot decide or are not sure, then I personally would go with 20% international. This is what Vanguard used to recommend. Then they went to 30% and I think they are now at 40%. The 20% comes from a number of sources that say you should not have more than 20% in international and other that say you should not have less than 20%.
If in your IPS you have determined you want to go with (say) 40% international, then other sources and research suggest you should not be aggressive in rebalancing. Maybe wait until the larger percentages of your allocation are 5% off the target. So, in that case, rebalance when international is at 35%.