If you're here, then you should already know what a wargame is. If you don't, an explanation can be found here. This page is designed to be used as a brief overview on various wargames and wargame related topics, each having their own dedicated page.
Bolt Action is a 28mm wargame made by English game company Warlord Games set during WWII, with enough varied content to represent every theatre of war. The game's design is built around the enjoyment of the game over historically accurate (but unfair) decisions, but the attention to detail with each nation's specific units and their strengths and weaknesses does provide a very authentic WWII feel, and those not familiar with every miniscule detail wouldn't know the difference. The game focuses on platoon-sized forces with a larger focus on infantry than tanks, but if you find tank combat a lot more interesting, then you may find the Tank War supplement to be of some interest.
Black Powder is a 28mm wargame (Although some say the rules work better on a larger scale of conflict at 15mm, Warlord Games advertises it as 28mm and provides 28mm troops and accessories) covering a variety of battles from the dawn of the 18th century to the close of the 20th century - the most well-known battles from this era being the American War of Independence (1775-1783), the Napoleonic Wars (1803-1815), the American Civil War (1861-1865), and the Anglo-Zulu War (1879) just to name a few. I can't say much for how Black Powder plays technically, but I do know that it's incredibly different from Bolt Action thanks to the rank-and-file aspects of warfare during that time. It's made by the same company that made Bolt Action, Warlord Games.