Cracks in Ceiling/Uneven floors

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Hello fellow BP members, I just walked through a small 3/1 house in Glendora and noticed cracks in the ceiling in 2 rooms on either side of the house and a crack in the wall near the front of the house. The floors also seemed uneven at times, I thought I was imagining things so my wife walked with me and confirmed that the floors seem to slope in some rooms. The house was built in the 20's I believe but I'd have to double check. What could cause this? Is this a "red flag" ?