This is for people that live in another country (not the US) and want to login directly into the in US english homepage or for people that don't like their regional Yahoo/Google homepages.
You can enter this address, it will take you straight into Yahoo's US homepage: https://www.yahoo.com/?p=dnr
You can enter this address, it will take you straight into Google's US homepage: https://www.google.com/ncr
That will hopefully avoid Yahoo and Google from redirecting you.
If you don't want to memorize it you can create a shortcut in your browser, then edit it and put the address above for each site.