Short answers, pulled from the story.
The Kingdom of Jerusalem was founded in 1099 following the First Crusade and lasted until 1291, when Acre fell to the Mamluk sultan al-Ashraf Khalil. Its nearly 200-year existence was divided into two periods: the original kingdom, which fell to Saladin in 1187, and the re-established Kingdom of Acre, which ran from 1192 to 1291.
Godfrey of Bouillon became the first ruler of the Kingdom of Jerusalem after a council held in the Church of the Holy Sepulchre on the 22nd of July 1099. He declined the title of king, taking instead the designation Advocatus Sancti Sepulchri, defender of the Holy Sepulchre. His brother Baldwin of Boulogne succeeded him in 1100 as the first to formally claim the title of king.
The Kingdom of Jerusalem was ethnically, religiously, and linguistically diverse. The ruling class was predominantly French-speaking Catholic Crusaders. The majority of the population consisted of native Christians, including Greek and Syriac Orthodox, as well as Sunni and Shi'a Muslims. There were also small communities of Jews and Samaritans; the traveller Benjamin of Tudela estimated around 1,200 Jews and at least 1,500 Samaritans in the kingdom around 1170.
The kingdom's army was destroyed at the Battle of Hattin on the 4th of July 1187. The defeat resulted from internal political divisions, particularly the conflict between Guy of Lusignan and Raymond III of Tripoli, combined with Raynald of Chatillon's raids that had broken truces with Saladin. After Hattin, Saladin rapidly overran the kingdom; only the port of Tyre remained in Crusader hands.
Emperor Frederick II arrived on the Sixth Crusade in September 1228 and negotiated a ten-year truce with Ayyubid sultan al-Kamil, signed in February 1229. The agreement restored Jerusalem, Bethlehem, Nazareth, and surrounding castles to Christian control in exchange for the truce and guaranteed freedom of worship for Muslim inhabitants. Frederick was excommunicated at the time, and the Patriarch of Jerusalem placed the city under interdict in protest at the treaty's terms.
Venice and Genoa were essential to the Kingdom of Jerusalem's survival. Their naval power transported troops, food, and goods, and their financial resources funded military campaigns. The kingdom's dependence on the Italian maritime republics grew over time, especially after the capital moved to the port city of Acre. Their rivalry ultimately erupted into the War of Saint Sabas in 1256, a military conflict fought in Acre and the wider region that further destabilised the already weakened kingdom.