As long as the Muslim population remains around 1% of any given country they will be regarded as a peace-loving minority and not as a threat to anyone. In fact, they may be featured in articles and films, stereotyped for their colorful uniqueness.
At 2% and 3% they begin to proselytize from other ethnic minorities and disaffected groups 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.
They will push for the introduction of halal (clean by Islamic standards) food, thereby securing food preparation jobs for Muslims. They will increase pressure on supermarket chains to feature it on their shelves -- along with threats for failure to comply.
At this point, they will work to get the ruling government to allow them to rule themselves under Sharia, the Islamic Law. The ultimate goal of Islam is not to convert the world but to establish Sharia law over the entire world.
When Muslims reach 10% of the population, they will increase lawlessness as a means of complaint about their conditions ( Paris --car-burnings). Any non-Muslim action that offends Islam will result in uprisings and threats ( Amsterdam - Mohammed cartoons).
After reaching 20% expect hair-trigger rioting, jihad militia formations, sporadic killings and church and synagogue burning.
At 40% you will find widespread massacres, chronic terror attacks and ongoing militia warfare.
From 60% you may expect unfettered persecution of non-believers and other religions, sporadic ethnic cleansing (genocide), use of Sharia Law as a weapon and Jizya, the tax placed on infidels.
After 80% expect State run ethnic cleansing and genocide.
100% will usher in the peace of 'Dar-es-Salaam' -- the Islamic House of Peace -- there's supposed to be peace because everybody is a Muslim:
Of course, that's not the case. Muslims then start killing each other for a variety of reasons.
Edited for brevity, from What Islam Isn't; see the original for lists of percentages and countries.