Bitcoin has a fixed total supply when all Bitcoin is mined.  The halving does not reduce this supply, it only reduces the upcoming influx of coins to the market. 

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Bitcoin has established its dominance ever since.  Although there are lots of new altcoins coming to challenge the dominance of Bitcoin, they all fell short due to the fact that Bitcoin had established its ground and people are somehow contented on the features Bitcoin gives especially being the best in network security.  There may be more advanced technology out there but the flaw in that altcoin security makes Bitcoin shine more.

I believe this is the advantage of being the first cryptocurrency to be greatly adopted and recognized by the government, they will have the most volume in the market and thus ca be said that Bitcoin is the king of cryptocurrency.