It's not clear what you need help with - something to use as a board (ie., a sheet of cardboard), or how to design a new board game?
I will assume the latter, and that your teacher wants to see a result that demonstrates learning about the topic (WWI).
A simple approach is to 'copy' the Trivial Pursuit idea and make it a trivia game. Collect as many facts as you can from your text books, class notes, and/or Wikipedia (see ref below). Convert them into questions, preferably with 3 multiple choice answers, and write them on one slips of paper - use Post-it notes and cut off the sticky part if can't find anything else suitable. Write the correct answers on the back.
Can you collect and make 100 questions...?
Don't do an exact replica of Trivial Pursuit for the board - keep it much simpler. Design on spare paper first before doing final artwork on a piece of cardboard. Create four 'ladder' tracks (assuming up to 4 players) with 11 spaces in each, numbered 0 - 10, about 1 inch square. (If you can only gather 50 questions, then make the tracks go to 5 or 6 instead.)
Use buttons for pieces to move on the tracks, or other coloured tokens borrowed from Monopoly (or similar), or even better -little plastic soldiers that you can paint different colours to tell who owns which piece.
Consider modifying the track drawings to look like WWI trenches, to add a sense of theme. At the end of the trench track (at Number 10), label the spaces collectively as "Peace".
Create one extra card for every player called "Over the Top".
Play is simple and goes clockwise. Another player reads a question for you. If you get it right, move ahead one space on your track. Wrong: Don't move (no going backwards in this simple version).
A player has one "Over the Top" (OtT) card each. After hearing a question, but before answering it, they may choose to play their OtT. If they get the question right, they jump ahead 2 spaces instead of 1. Whether they get it wrong or right, their OtT is spent. To make the game go faster, a player may get back their OtT card after they get past halfway along their trench.
First player to 'Peace' is the winner.