ONE OF the most brutal but least-known battles against Islamic State-affiliated militants has been underway for eight years in the Sinai Peninsula. In that desert landscape, Egyptian military and police forces have consistently failed to eliminate an insurgency rooted in deprivation and other local grievances. Their tacits, which have included mass roundups, the bombing and shelling of civilian areas, and the eviction of tens of thousands of people from their homes, have killed thousands, and thousands more have been arrested and tortured. The war has gone international: Israel is believed to have carried out scores of its own airstrikes on Egyptian territory.