Are Vista's needed for an American to cross into Croatia, Bosnia, Montenegro, Albania, or Slovenia?

Visa, no. Limited to 90 days and a few require you have 3 months left on your passport. Land borders can be slow at times. Croatia/Montenegro has been known to back up for instance.

Hello,
Thank you for the info and for your time in answering my question. Have a great day!!

Ann,

I'm assuming you're referring to a Visa. This website may help - https://www.schengenvisainfo.com/non-eu-countries-where-you-can-go-with-schengen-visa/ .

While you shouldn't have any trouble entering the countries you mentioned, be sure to allow time at border checkpoints as you'll have to clear those every time you enter a different country. It's been a few years but as I recall, entry from Croatia to Bosnia or vice versa requires a border check and likely the same with other countries. I vaguely recall some type of border checks and Passport stamps between Slovenia and Croatia as well.

Are you going to be driving or taking public transport?

The answers you have gotten are correct, but never trust this forum or any forum for such advice. Go to the country's consulate page to be sure you have the correct answer for such an important question.

I have been to all those borders within the past 2 weeks and US passport was all I needed, which should increase confidence in previous anseers