The Crusader states were a number of mostly 12th- and 13th-century feudal states created by Western European crusaders in Asia Minor, Greece and the Holy Land, and during the Northern Crusades in the eastern Baltic area. The name also refers to other territorial gains (often small and short-lived) made by medieval Christendom against Muslim and pagan adversaries.

Beginning in the 7th century Muslim rulers began expanding their territories into Christian Roman/Byzantine lands conquering Egypt and the Levant and gradually taking over all of North Africa, much of Southwest Asia, and most of the Iberian Peninsula. The Eastern Romans, or Byzantines, partially recovered lost territory on numerous occasions but over time gradually lost all but Anatolia and parts of Thrace and the Balkans. In the West the Roman Catholic kingdoms of northern Iberia launched a series of campaigns known as the Reconquista to reconquer the peninsula from the Arabized Berbers known as Moors (who called it al-Andalus). The conquered Iberian principalities are not customarily called Crusader states, except for the Kingdom of Valencia, despite fitting the general criteria.

Amalric I of Jerusalem (also Amaury or Aimery) (1136 – 11 July 1174) was King of Jerusalem 1163–1174, and Count of Jaffa and Ascalon before his accession. Amalric was the second son of Melisende of Jerusalem and Fulk of Jerusalem, and succeeded his older brother Baldwin III. During his reign, Jerusalem became more closely allied with the Byzantine Empire, and the two states launched an unsuccessful invasion of Egypt. Meanwhile, the Muslim territories surrounding Jerusalem began to be united under Nur ad-Din and later Saladin. He was the father of three future rulers of Jerusalem, Sibylla, Baldwin IV, and Isabella I.

Amalric was born in 1136 to King Fulk, the former count of Anjou who had married the heiress of the kingdom, Melisende, daughter of King Baldwin II. After the death of Fulk in a hunting accident in 1143, the throne passed jointly to Melisende and Amalric's older brother Baldwin III, who was still only 13 years old. Melisende did not step down when Baldwin came of age two years later, and by 1150 the two were becoming increasingly hostile towards each other. In 1152 Baldwin had himself crowned sole king, and civil war broke out, with Melisende retaining Jerusalem while Baldwin held territory further north. Amalric, who had been given the County of Jaffa as an apanage when he reached the age of majority in 1151, remained loyal to Melisende in Jerusalem, and when Baldwin invaded the south, Amalric was besieged in the Tower of David with his mother. Melisende was defeated in this struggle and Baldwin ruled alone thereafter. In 1153 Baldwin captured the Egyptian fortress of Ascalon, which was then added to Amalric's fief of Jaffa (see Battle of Ascalon).