The Kharidian Empire was founded in Second Age by Elidinis, Tumeken, Amascut and Icthlarin in the Second Age. The Empire's lands were located in the land currently known as the Kharidian Desert.
The Kharidian Empire built cities and big structures all over the desert, most notably the still-standing Emir's Arena.
Second Age
During the Second Age, the peace of the desert became threatened, when Zaros sought to expand his already large empire into the Menaphite territory, ruled over by the Kharidian Empire. Thus began a long and bloody conflict known as the Kharidian-Zarosian War. Elidinis, Tumeken, Amascut, Icthlarin and the rest of the pantheon fought to defend their lands, but even together they lacked power to push back the Empty Lord. The Kharidian Empire's lands were captured bit-by-bit as the invaders slowly but surely pushed farther into its lands.
Eventually, as the situation became dangerously dire, Icthlarin and Amascut went looking for allies to help them defeat the mighty Zarosian army. They eventually wandered off to the war-torn world of Freneskae, home to the powerful and near-immortal race of Mahjarrat. Icthlarin managed to convince a number of them to join and help defend the Kharidian land from the invading Zarosians.
Soon after that, Icthlarin, Amascut and the Mahjarrat returned to Gielinor. With the Mahjarrat on the Kharidians' side, the tide of war began to change as the Mahjarrat - dubbed the "Stern Judges of Icthlarin" by the Kharidian defenders - quickly began decimating Zaros' forces. For the first time since the beginning of the war, the Kharidians were on the offensive side, quickly gaining more power over the Zarosians.
Under the leadership of Icthlarin, the united army of the Mahjarrat and Kharidians began pushing back the Zarosians' invasion attempt and started taking back their lost lands. All lost lands were soon reclaimed, but a new threat was creeping up that Icthlarin hadn't seen coming: With the war over, the Mahjarrat grew restless, and eventually their allegiance shifted to Zaros.
Third Age
In the Third Age, the Kharidian Empire was mostly unaffected for the first three millenniums, perhaps due to an alliance Elidinis made with Saradomin. However, during the last millennium of the God Wars, Zamorak launched a massive invasion against the Kharidians called the Kharidian Desert Campaign, which would lead to the fall of Uzer and later Ullek. It is unclear whether the Kharidian Empire was disbanded. This may have happened at the end of third age, when Guthix woke and banished the gods from Gielinor. Tumeken and Elidinis were forced to leave Gielinor. Amascut and Icthlarin could stay, because while they were created from the divine essence of both Tumeken and Elidinis, they were far less powerful than true gods.