The first bitcoin mining difficulty increase happened

On December 30, 2009, the first-ever increase in mining difficulty happened.
 

Bitcoin’s mining difficulty is a measure of how hard it is to find a new block compared to the easiest it can ever be. It is recalibrated roughly every two weeks to ensure that the time between blocks remains around 10 minutes, as per the design of Bitcoin’s creator, Satoshi Nakamoto.
 

Initially, Bitcoin’s difficulty was set at 1, which is the lowest possible value. However, as more miners joined the network and started contributing their computing power, the difficulty needed to be adjusted to keep the block discovery rate consistent.
 

On that historic day, the difficulty rose from 1 to 1.18 with the mining of block 32256. Although this was a modest increase, it was the first of many adjustments that would follow as Bitcoin continued to gain popularity and attract more mining activity.