Islam contains a key tenant called Sharia Law, 

which is a form of government

Once Islam achieves a majority in an area, its followers often implement Sharia Law, which is NOT tolerant of other religions.  Non-followers are called Infidels.  Government Force can be used to penalize or eliminate other religions.  (This directly contradicts the US Constituion, which protects the right of citizens to choose their religion.)

Islam Uses Coercion to Spread

Historical methods of conversion to Islam occured across different regions and eras in the 7th–18th centuries and beyond. Muslim rulers typically sought political dominance and revenue (via the jizya tax on non-Muslims) rather than immediate mass conversion. Instead, conversion (Islamization) unfolded as a socio-cultural process over generations through a combination of exposure to the faith and practical incentives.

Some of the methods used to spread Islam: 

• Military conquest and subsequent rule. Early rapid expansions (632–750 CE) under the Rashidun and Umayyad caliphs created vast Muslim-governed territories. Over time the dominant Islamic administration, Arabic language, and legal system encouraged gradual, voluntary shifts to Islam for practical reasons.

• Trade and commercial networks: Muslim merchants (starting with Muhammad himself) carried Islam along trade routes like the Silk Road, Indian Ocean, trans-Saharan paths, and Southeast Asian maritime routes. They built communities, demonstrated ethical business practices, and introduced the faith organically. This was especially effective in West Africa, India, Indonesia, and East Africa, where conversion often followed commercial ties rather than conquest.

• Intermarriage and family/social integration: Marriages between Muslims and non-Muslims frequently led to conversions of spouses and children. Muslim communities integrated locally, and over generations, social ties, shared festivals, and daily life encouraged gradual adoption of Islam.
   

• Economic and social incentives: Converts were exempt from the jizya tax paid by non-Muslims (dhimmis), gained access to administrative/military roles, and enjoyed greater social mobility under Muslim rule. In some cases, this included escaping debt, humiliation, or legal restrictions. Pragmatic factors like political allegiance or career advancement played a role, especially in early centuries when full Arabization was sometimes required for converts (via the mawla client system).
   

• Political alliances, diplomacy, and influential conversions: Tribal leaders, kings, or elites converting brought their followers en masse (e.g., Berber or Turkic tribes). Treaties, marriages, and alliances with Muslim powers facilitated this. In West Africa and Southeast Asia, rulers adopted Islam to strengthen trade or state-building, leading to broader Islamization.
   

• Migration and settlement of Muslim communities: Arab, Persian, or later Muslim migrants established urban centers, mosques, and schools. Their presence, combined with cultural prestige during the Islamic Golden Age (advances in science, philosophy, and justice), made Islam attractive to locals seeking opportunity or intellectual engagement.
   

• Da'wah (peaceful preaching and invitation): From the time of Muhammad onward, Muslims actively invited others to Islam through personal example, sermons, Quran recitation, and missionary outreach.
   

Notes on context: Conversion was often slow (Muslims remained a minority in many conquered areas for 200+ years). In places like India or sub-Saharan Africa, it involved "mixing" with local customs before full adoption. 

Kidnapped Priests and Christian Civilians Held by Islamists in Nigeria