I guess Riley has been to...
>! Newark, or [Newark-on-Trent][1], England.

_My prefix is unused._
>! We called an unused thing as "a **new** thing".

_My suffix is a forest removed._
>! The flood is coming, cut down all the woods to make an **ark**!

_My infix is a reunited analogue._
>! Unite all the manpower to engage a **war**.

_I am all alone but for a dog._
>! Well, there is _one_ new built ark, so it is _alone_. 
>! <br>
>! However, there is a [place][2] that held a [dog show][3] not far from the downtown area.

[1]: https://en.wikipedia.org/wiki/Newark-on-Trent
[2]: 
https://www.google.com/maps/place/Newark+Showground/@53.0800884,-0.8095732,13.5z/data=!4m5!3m4!1s0x48784b3d4ebfad3b:0x26919ac4feb35d37!8m2!3d53.098385!4d-0.768045
[3]: http://www.allaboutdogsshow.co.uk/newark/