Short answers, pulled from the story.
The Soviet Union ordered the entire Chechen people to leave their homes and forced them onto trains sent to Kazakhstan and Kyrgyzstan under false accusations of collaborating with Nazi Germany. Estimates suggest between one-quarter and one-third of the deported population perished within the first four years of resettlement.
On the 7th of August 1999, Shamil Basayev led two groups of up to 2,000 fighters into the neighboring Republic of Dagestan. These forces included Chechens, Dagestanis, and Arab mujahideen who aimed to establish an Islamic state in the region before being routed by Russian troops by mid-September 1999.
Sixty-two people died in an apartment building housing families of Russian soldiers on the 4th of September 1999. Over the next two weeks, bombs targeted three other buildings and a mall resulting in more than 350 deaths in total.
Amnesty International reported that Chechen civilians were purposely targeted in apparent disregard for humanitarian law with thousands of forced disappearances occurring between 1999 and 2008. Western groups estimate about 5,000 people went missing during this period while mass graves containing hundreds of corpses have been uncovered since the start of the war.
Doku Umarov declared the creation of the Caucasus Emirate in October 2007 after stating in April 2006 that they no longer planned negotiations. He urged for a global Jihad and created a political schism between moderates and radical Islamists.