Joining Multiple Dataframes on columns if sets of columns are (partly) different

Question

I need to unite several dataframes into one. Here are the original dataframes df1, df2, df3:

df1 = DataFrame(cfd1)
df1
         v1   v2  v3
case_1  197  338  15
case_2  163  293  19

df2 = DataFrame(cfd2) # v4 instead of v3
df2
         v1   v2  v4
case_3  197  338  15
case_4  163  293  19

df3 = DataFrame(cfd3) # v5 instead of v3/v4
df3
         v1   v2  v5
case_5  197  338  15
case_6  163  293  19

Here is the desired output (df_united):

df_united
         v1   v2  v3  v4  v5
case_1  197  338  15 NaN NaN
case_2  163  293  19 NaN NaN
case_3  197  338 NaN  15 NaN
case_4  163  293 NaN  19 NaN
case_5  197  338 NaN NaN  15
case_6  163  293 NaN NaN  19

How to do this?

Any help will be greatly appreciated.