Islam started when prophet Mohamed peace be upon him received his first revelation about 1440 years ago in Makkah
Prophet Mohamed is Arabic, his teachings are to all humanity.
In recent times Indian immigrants to Arabia have brought Hinduism with them and Filipino immigrants have brought Roman Catholicism with them. (While Christianity does have a historic presence in Arabia, Catholicism specifically never did.) However, prior to modern immigration, Arabia remained almost exclusively Muslim. (It is predominantly Sunni Muslim with Twelver Shiite Muslims along the northern Persian Gulf coast, Zaydi Shiite Muslim in northern Yemen, and Ibadi Muslims in Oman.)
The main prophet of Islam who brought down the teachings that lead to the Quran was born in Mecca in Saudi Arabia.
Muhammad, the final prophet of Islam and the Revealer of the Qur'an, brought the teachings of Islam to all of Arabia. However, Islamic tradition holds that Hud and Saleh came to the communities of 'Ad and Thamud, which were city-states within Arabia, centuries if not millenia before Muhammad and taught the principles of monotheism.
Islam did start in the so-called "Saudia-Arabia";
Islam spread from Arabia.
Many people believe that the religion of Islam was founded by the Prophet Muhammad (peace be upon him) in the land of Arabia. However, Muslims believe that all the prophet's brought the religion and message of Islam and hence there is no single one place where Islam was founded.
Traders in Africa had contact with Arabia and converted to Islam
The main religion of Saudi Arabia is Islam
No, Islam began in Mecca city in current Saudi Arabia country. but later Iran absorbed Islam and highly supported and developed it. Islam is Iran is Shia Islam and in Saudi Arabia is mostly Sunni Islam.
Saudi Arabia
In Arabia the city of Mecca which is part of Saudi Arabia.
Islam, specifically Wahhabi Sunni Islam.