The Persian Empire was a series of historical empires that ruled over the Iranian plateau, the old Persian homeland, and beyond in Western Asia, Central Asia and the Caucasus. The Persian empire has become what we know today as Persia or more commonly, Iran. The most widespread entity considered to have been a Persian Empire was the Achaemenid Empire (550–330 BC), a united Iranian kingdom that originated in the region now known as Pars province of Iran. Most of the successive states in Greater Iran prior to March 1935 are collectively called the Persian Empire by Western historians. Virtually all the successor empires of Persia were major regional and some major international powers in their day.