Young countries
The 21st century is advancing at a frenetic pace, to the point that events that occurred just a few years ago seem to have happened an eternity ago. Believe it or not in just two decades since the 21st century started five sovereign countries were created. These are the five youngest countries on Earth.
South Sudan (2011)
South Sudan was created after an independence referendum took place between 9 and 15 January 2011. During the referendum a whooping 98.83% of the population voted in favor of their independence, and after a few months of reorganization and preparation on 9 of July of 2011 the country declared its independence and sovereignty.
This was the result of an extremely bloody decades-long civil war which ended after a shaky peace agreement took place in 2005. South Sudan then became the 54th country in Africa and a bit later the 193rd member of the United Nations in July 14 2011.

Sadly the future of this young landlocked nation is currently uncertain since just 2 years after its independence a new civil war exploded in December 2013 after a political power struggle broke out between President Kiir and his former deputy Riek Machar, sinking the young and newly formed country into a new and even bloodier civil war.
Kosovo (2008)
Kosovo is another young country created as a result of an extremely bloody civil war, and perhaps one of the most internationally famous wars of the late 20th century: the Kosovo War (Mar 5, 1998 – Jun 11, 1999). The Kosovo War is famous mainly because NATO saw itself involved in it during the bombing of Yugoslavia, a massive air striking campaign aimed at stopping the Serbian mass slaughter of Albanian civilians.
Long after the war was over, in February 17 2008, Kosovo unilaterally declared its independence from Serbia after a long process which started in 2005. Many U.N. member states including the United States of America promptly recognized the young country as a sovereign national entity. Since then Kosovo has been bidding for its entry into different international organizations, including the U.N. itself.

Serbia (2006) and Montenegro (2006)
Kosovo wasn’t the only country to reform and declare its independence after the Kosovo War. Serbia and Montenegro was a national unity formed as a single sovereign nation after the collapse of Yugoslavia. This supranational union was rocky from the start, as we can clearly see in the many changes its constitution suffered during its short life. Eventually, after a referendum which took place on May 21, 55.5% of the population of Montenegro voted to leave the union and form their own sovereign and independent country without Serbia. Montenegro’s independence was peaceful and promptly recognized by the Serbian parliament.
Exactly two days later Serbia itself elevated its own declaration of independence, declaring itself as a new national entity independent from its previous form. Interestingly, as we can see the Kosovo War created not one but three different countries and saw the disappearance of Yugoslavia as a nation.

Timor-Leste (East timor) (2002)
Lastly, the first country to be formed during the 21st century: Timor-Leste, more commonly known in the West as East Timor. Unlike the other examples in this list where the transition from being a territory belonging to another nation into becoming a free sovereign country was relatively smooth, the transition of East Timor into the Democratic Republic of Timor-Leste was violent and chaotic.
In 1999 this Southeast Asian territory started a referendum among its population in order to bid for its independence. The referendum was a success among the people of East Timor and the young nation quickly declared its sovereignty from Indonesia.
Immediately after the declaration of independence violent pro-Indonesia militias started taking over the streets and even reached Dili, the capital of the young nation. Luckily a joint task force deployed by the U.N. managed to control the situation and East Timor, now called Timor-Leste, finally managed to become independent on May 20 2002.
Timor Leste joined the U.N. that same year as its 191st member.