I'm struggling with factoring. Some are really easy, and some I don't know where to start.

m^{3}-mn^{2}+m^{2}n - n^{3}+ m^{2}- n^{2}is one that I need to factor.

The answer is (m+n)(m-n)(m+n+1) and if I multiply it all out, it gets me back to the original.

I get that (m+n)(m-n) is (m^{2 }- n^{2}). Do the substitution and you get m^{3}-mn^{2}+m^{2}n - n^{3}+ (m+n)(m-n).

You can factor m^{3}-mn^{2}+m^{2}n - n^{3 }into (m^{2}-n^{2})(m+n), and further into (m+n)(m-n)(m+n).

Substitute again and you get (m+n)(m-n)(m+n) + (m+n)(m-n). Then I don't know where to go.

Can someone point me in the right direction?

Thanks