Qatar celebrates its National Day on 18 December each year – the date in 1868 on which it was first given informal recognition of its autonomy.
Prior to 1868 it had been ruled by the Al Khalifa family of Bahrain and assumed to be subject to Bahraini rule. (Doha was even bombarded by the East India Company in 1821 because the Al Khalifa had signed an agreement not to engage in piracy, but failed to ensure the agreement was observed by the Qataris.)
But in 1867 the Bahrainis sent a large naval force to put down a rebellion by the Qataris, in violation of their 1820 agreement with the East India Company which gave the United Kingdom overall authority in the Gulf. The British Political Agent, Colonel Lewis Pelly, intervened in December 1868 (why the delay? Maybe, in time-honoured British diplomatic fashion, he was monitoring the situation…) and asked for negotiations, not just with the Bahrainis, but with a Qatari representative too – Muhammad ibn Thani ibn Muhammad. The al-Thani family have ruled Qatar ever since.
Qatar didn’t achieve full sovereignty until 1971; it was a protectorate under the Ottoman Empire until 1913, then a British protectorate within the so-called Trucial States along with what are now the United Arab Emirates. But 18 December remains the National Day.