The surge in altcoins has led many traders to forecast the dawn of a new altcoin season. According to "The Moon" a pseudonymous Twitter analyst, altcoin seasons follow a major run-up in the price of BTC, especially when the price stalls or pulls back.
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yes, this dominance of the crypto market gives Bitcoin a lot of influence and control over altcoins. often happens as you say when there is an uptrend in the market the first trigger is Bitcoin and other altcoins following an uptrend. Altcoin prices are closely related to Bitcoin prices, Altcoins often follow Bitcoin price movements with small to large differences, even reaching prices that are many times the previous Altcoin price.Reference