At 1% muslim population, a nation typically experiences some terrorism.
At 2% to 5%, they begin to proselytize from other ethnic minorities and disaffected groups, often with major recruiting from the jails and among street gangs.
From 5% on, they exercise an inordinate influence in proportion to their percentage of the population. At this point, they are seen to work to get the ruling government to allow them to rule themselves (within their ghettos) under Sharia, the Islamic Law. The ultimate goal of Islamists is to establish Sharia law over the entire world.
When Muslims approach 10% of the population, they tend to increase lawlessness as a means of complaint about their conditions.
After reaching 20%, nations experience hair-trigger rioting, jihad militia formations, sporadic killings, and the burnings of Christian churches and Jewish synagogues. At 40%, nations experience widespread massacres, chronic terror attacks, and ongoing militia warfare...
Update: this link has been censored: http://www.examiner.com/article/as-muslim-population-grows-what-can-happen-to-a-society ;
but the gist of the article is still available here: https://247sports.com/college/usc/Board/59419/Contents/As-Muslim-population-grows-what-can-happen-to-a-society-41331804/