Although O'Hare is the second busiest airport in the world, it's much more of a domestic hub than an international one. Other large airports around the world serve far more international passengers than O'Hare.
From ACI Website
MONTHLY - JANUARY 2006
RANK CITY PASSENGERS % CHG
1 LONDON, GB (LHR) 4 630 676 0.2
2 PARIS, FR (CDG) 3 676 333 6.5
3 HONG KONG, CN (HKG) 3 403 000 15.8
4 FRANKFURT, DE (FRA) 3 160 177 (0.0)
5 AMSTERDAM, NL (AMS) 3 025 243 2.5
6 SINGAPORE, SG (SIN) 2 676 224 12.6
7 BANGKOK, TH (BKK) 2 560 258 23.1
8 DUBAI, AE (DXB) 2 346 455 17.1
9 SEOUL, KR (ICN) 2 248 245 4.7
10 TOKYO, JP (NRT) 2 180 688 (0.8)
11 LONDON, GB (LGW) 1 812 594 1.7
12 MADRID, ES (MAD) 1 683 078 6.6
13 TAIPEI, TW (TPE) 1 560 818 15.2
14 TORONTO, ON, CA (YYZ) 1 445 809 2.8
15 LOS ANGELES, CA (LAX) 1 436 575 (0.5)
16 NEW YORK, NY (JFK) 1 387 743 (0.6)
17 LONDON, GB (STN) 1 332 698 7.1
18 MIAMI, FL (MIA) 1 317 402 2.1
19 MUNICH, DE (MUC) 1 315 826 11.6
20 MILAN, IT (MXP) 1 276 398 11.2
21 DUBLIN, IE (DUB) 1 252 397 13.0
22 KUALA LUMPUR, MY (KUL) 1 220 444 20.6
23 COPENHAGEN, DK (CPH) 1 217 878 5.2
24 ZURICH, CH (ZRH) 1 204 871 (0.4)
25 SHANGHAI, CN (PVG) 1 188 455 4.9
26 MANCHESTER, GB (MAN) 1 062 514 (1.1)
27 ROME, IT (FCO) 1 037 437 4.8
28 VIENNA, AT (VIE) 1 030 859 9.8
29 BRUSSELS, BE (BRU) 998 810 1.8
30 SYDNEY, AU (SYD) 970 028 (1.5)