War started 4 days ago, when Recep Tayyip Erdoğan ordered his puppet Aliev to attack Armenia. The Azeri army with the help of Turkey and Syrian National Army militants launched an unprovoked attack on the Republic of Artsakh (which is historically regarded as a part of Armenia since 7th century BC).
The population of Armenia is just 3 million, compared to 100 million plus for Azerbaijan and Turkey. Israel is providing the latest weapons to Azerbaijan, who purchase them using petro-dollars. Armenia doesn't have any petroleum resources and most of its budget is comprised of remittance from its large diaspora. Armenia is surrounded on all sides by hostile neighbors.
The reason for the war: The modern Armenia comprises of only around 10% of the historic Armenian homeland. The remainder is currently controlled by Turkey, who committed one of the most brutal genocides in the history of mankind, when they exterminated 2 million Armenians, along with 2 million other Christian minorities (Greeks, Assyrians.etc) during 1915-18. Now Erdogan want to cleanse the remaining 10% and completely exterminate the Armenian nation.
Now this is just a start. Erdogan wants to be the Caliph of his dream Turkic empire, which comprises of Anatolia, Caucasus, Balkans, Siberia, Levant, Central Asia and the Middle East.
Current situation: The Armenian soldiers are more battle-hardened, but Azerbaijan is having the latest weapons. So far Armenia have lost large swathes of territory, but during the last couple of days they have managed to stall the Turkish/Azeri advance.
US-made weapons are also being used in this war. Yesterday, a Turkish F16 fighter jet shot down an Armenian fighter jet inside Armenian borders. The pilot was killed.
Till yesterday, the Armenians have admitted that their confirmed casualties include 104 soldiers and 7 civilians who are dead. Azerbaijan hasn't released the details of military deaths.