I intend to do classification modelling, but my target variable has only one value
Assuming I can’t use external datasets, what’s the solution to this problem? How can I best understand those who have defaulted if I don’t have something to compare them to?


If you wanna use this only this data as classification task, you can't perform this task. You could way this around, by generated fake data with label 0(you think about which value of parameters comes to default).

But you could try clustering algorithms(like k-means) and find the groups of specific clients. Perhaps one of these groups its group of default.