20th century BC

(21st century BC - 20th century BC - 19th century BC - other centuries)

(3rd millennium BC - 2nd millennium BC - 1st millennium BC)

• 2064 - 1986 BC -- Twin Dynasty wars in Egypt
• 1991 BC -- Egypt: End of Eleventh Dynasty, start of Twelfth Dynasty
• 1932 BC -- Amorite conquest of Ur
• 1913 - 1903 BC -- Egyptian-Nubian war
• 1900 BC -- Achaean invasions of Greece
• around 1900 BC -- Fall of last Sumerian dynasty

• 1950 BC -- The copper bar cubit of Nippur defines the Sumerian cubit as 51.72 cm