Most important motives behind the Arab expansion

In your opinion, what were the most important motives behind the Arab expansion: Economic, religious or cultural?

Using secondary sources from Bernard Lewis and Ira Lapidus in Western Civilization by Dennis Sherman Vol 1 eight edition

Write about why some countries preferred to be conquered by the Arabs than the Persian or Byzantine.

How Arabs did not force people to convert to Islam.

Byzantine and Persia over taxed countries they conquered