Here is the list of no duplicate Modern War codes for alliances:
561 663 257
939 737 240
943 155 896
767 026 498
176 376 695
538 666 786
680 687 899
808 604 522
329 568 911
837 595 700
680 332 248
896 176 816
215 017 424
676 014 689
178 564 774
700 060 857
747 217 693
178 344 453
378 246 089
192 181 303
985 994 820
404 336 889
921 467 639
758 055 886
688 578 684
734 985 465
425 220 156
304 861 124
776 091 031
471 285 588
256 430 325
707 855 276
602 726 210
888 357 422
792 648 868
There is an even bigger list of over 1400 Modern War codes over at the official forums of the game so you could as well check it out and add all those codes if you want a huge alliance. Or simply post your code below if you want more people to add you!