Pakistan is a federal parliamentary republic in South Asia on crossroads of Central Asia and Western Asia. Economists estimate that Pakistan has been part of the wealthiest region of the world throughout the first millennium CE [because it was part of India] having the largest economy by GDP. This advantage was lost in the 18th century as other regions edged forward such as China and Western Europe. For further information on the types of business entities in this country and their abbreviations, see "Business entities in Pakistan".