This is an early 20th postcard showing "Kansas City 50 Years Ago". It's almost certainly Kansas City, Missouri & not Kansas City, Kansas across the river. I'm not 100% positive about that - I've only driven thru the cities on I-64 & that was a long time ago, and at least once it was as night. But I'll bet anything it's Missouri.
There is no indication of the actual date of the view in this postcard, but you can tell just by looking it was a while ago. The city looks like a small to mid-sized town mostly crowded next to the water, and there are open fields behind it, and steamboats on the river in front of it. I can tell just by looking at the front of the card that is early 20th century, made earlier than 1918 most likely. But the biggest clue is that it has a postmark on back - it was mailed from Kansas City, MO. to Ipswich, South Dakota on April 9, 1916. (To a Mr. Vick Olson, to be exact). So this card can be dated to 1916 at the latest, and probably a year or two earlier than that. It's a divided back card, so I know it was created in 1907 or later. So what we're looking at is an early 20th century rendition of a painting of the Kansas City skyline somewhere between the very late 1850s to mid 1860s. In the 1860s, this would have been a major population center for that part of the country.
I get all giddy about stuff like this, can't help it. It's just cool.
I have this listed on eBay - if you want to go to the listing, click here.