Swahili is the official language of Tanzania, but English is most often used in commerce. The government generally protects Christians from persecution, but they sometimes face persecution along the coastal areas, where large Muslim-majority populations have long traditions of Arab influence. The islands of Zanzibar and Pemba were once ruled by Oman, and after their independence they were annexed by Tanzania with the agreement they would be allowed to remain semi-autonomous. Christians on these islands face harsh persecution. Like many countries in Africa, there is a concerted effort by Arab countries to Islamize Tanzania by establishing Muslim businesses and schools throughout the country as well as electing Muslim officials into office and passing laws favoring Islam. The local churches in Tanzania are working to spread the gospel in difficult and unreached areas. The population is about half Christian and half Muslim, but only about 8 percent of the Christian population attends church. The Zanzibar archipelago region is 99 percent Muslim. Christians are persecuted by community members in Muslim-majority areas.