The Last Days of Dwarovar was a period of time (actually lasting over 1000 years) that led to the eventual decline of the Dwarven Empire due to the orcish incursion into Dwarovar, the dwarven underground network.
The last days began during the Fall of Er-navtir in 10,997 BL which was the dwarven hold responsible for maintaining the Dwarovar Highway, after the shutdown of the highway communication between the dwarven holds was largely lost and the once unified dwarven army became disorganised to put up a unified defense. The last days officially ended when the then capital Amldihr fell in 9,973 BL.
When the highway was shutdown long-distance communication was no longer possible and any dwarven armies in the field (aka in the halls, tunnels and highway) fell apart from disorganization and logistical problems, some like Harnul the Good, who was trapped in the middle of the Dwarovar tram system decided to continue on foot with his men to their original destination whilst others deserted for their homes and made new homes at nearby holds.
The lack of communication lead to the isolationalist stance we see from dwarven holds today, without any effective way of coordination between nearby holds, the surviving holds developed a defensive and independent attitude and often refused to make contact or even help outsiders, dwarf or otherwise.
Without food, water and goods coming in through the highway, many holds fell into chaos and starvation.
Initially, holds close to the surface fared better than their deeper counterparts, unlike deep holds which became increasingly isolationist and hostile, the outer holds became more reliant on outside relations and trade to sustain themselves. However, their reliance of the surface eventually made them vulnerable to blockade, especially during the time of the Phoenix Empire, luckily most outer holds had grown self-sufficient by then but as a consequence are now more selective with who they deal with.
On the extreme side, some dwarves decided to abandon the Dwarovar completely, the early dwarves establishing settlements and becoming kings and nobles over the less advanced inhabitants such as humans while some dwarves had a hand in the creation of many rising urban centres, establishing a strong dwarven mercantile class that still dominates today.