In 1901, Abdul Rahman’s son, Abdul Aziz (the future Ibn Saud), asked the Emir of Kuwait for men and supplies for an attack on Riyadh. Already involved in several wars with the Rashidis, the Emir agreed to the request, giving Ibn Saud horses and arms. Although the exact number of men waxed and waned during the subsequent journey, he is believed to have left with around 40 men.
In January 1902, Ibn Saud and his men reached Riyadh. With only a small force, he felt that the only way to take the city was to capture Al Masmak Castle and kill Ibn Ajlan, Chief of Riyadh. Ibn Saud’s force captured the castle and killed Ibn Ajlan according to plan, and took the city within the night.
1903–1907, Warfare period of sporadic battles ended with Saudi takeover of the al-Qassim region.
In 1913, with the aid of the Ikhwan, irregular raiders traveled mainly on camels and some horses, Ibn Saud captured Hasa from the Ottomans. Ibn Saud annexed Al-Hasa and Qatif into his domain of Emirate of Riyadh.
In December, the British government (started early 1915) attempted to cultivate favor with Ibn Saud via its secret agent, Captain William Shakespear, and this resulted in the Treaty of Darin.
The Battle of Jarrab was a territorial battle between the Al Sa’ud and their traditional enemies the Al Rashid in January 1915. It was a proxy battle of World War I between the British-supported Sa’udis and the Ottoman-supported Rashidis.
The main significance of the battle was the death of Ibn Sa’ud’s British Military Advisor, Captain William Shakespear.
The Treaty of Darin, or the Darin Pact, of 1915 was between the United Kingdom and Abdul-Aziz Al Saud (sometimes called Ibn Saud) ruler of Nejd, who would go on to found the Kingdom of Saudi Arabia in 1932.
The Treaty was signed on the island of Darin (also known as Tarout Island) in the Persian Gulf, on 26 December 1915 by Abdul-Aziz and Sir Percy Cox on behalf of the British Government.
The Treaty made the lands of the House of Saud a British protectorate and attempted to define its boundaries. The British aim of the treaty was to guarantee the sovereignty of Kuwait, Qatar and the Trucial States. Abdul-Aziz agreed not to attack these British protectorates, but gave no undertaking that he would not attack the Sharif of Mecca.
The Treaty was the first to give international recognition to the fledgling Saudi state. Also, for the first time in Nejdi history the concept of negotiated borders had been introduced. Additionally, although the British aim was to secure its Gulf protectorates, the Treaty had the unintended consequence of legitimising Saudi control in the adjacent areas. The Treaty was superseded by the Treaty of Jeddah (1927).
Source of the above: http://en.wikipedia.org/wiki/Treaty_of_Darin
[After Darin, he stockpiled the weapons and supplies which the British provided him, including a ‘tribute’ of £5,000 per month. After World War I, he received further support from the British, including a glut of surplus munitions. He launched his campaign against the Al Rashidi in 1920; by 1922 they had been all but destroyed.]
[ On the issue of succession, Ibn Saud stated that he would either appoint a successor himself or have a semi-public selection process. Cox preferred an inherited kingship which would reduce the unpredictability of an elected leader. ]
[Foreign Secretary to the Government of India, January 10,1916, PRO FO 371/2769 #41504.]