I would like to keep myself aware of Steam sale trends in order to know the games that are likely or not to be discounted in the future.
Is there a way to access Steam sales history globally and for a specific game?
Not on Steam itself. However, third party websites such as SteamDB exist specifically for this purpose.
I use a browser extension called Enhanced Steam that gives me lowest price ever, lowest price currently, and if the game has (or is) in a bundle.
It searches a variety of websites, not just Steam, and I can also access a graph of price history, so I can see what is happening with any price fluctuations.
If you're interested in a game on Steam and are interested in the price from anywhere you could try http://isthereanydeal.com.
I've always used https://www.steamprices.com/
It also has a graph to show sale prices and the date of them