Force sync Photos to iCloud on macOS I have recently been on holiday and saved all my photos on my mac whilst I was away. They didn't sync to iCloud as I wasn't connected to the Internet. 

I am back home now and setting up a new Windows laptop. The Windows laptop is showing all my Photo Stream pictures taken as of yesterday, but my holiday photos saved on the Mac doesn't seem to have synced to iCloud. The mac is now online and I have checked System Preferences → iCloud → Photos and it is all showing automatic sync, but this hasn't happened.

How can I force it to save these pictures on iCloud? I wish to get access to the holiday photos on my Windows laptop and remove all the data from the Mac.
On your Mac, open Photos and go to preferences under the Photo menu. Once in preferences select the iCloud tab at the top. In that window, there is an option to upload and store your photos on iCloud.