Force Works #21-22 and War Machine #24-25 are included to wrap up their respective series, because otherwise those issues would be orphaned unless placed in a volume of issues contained in the Avengers/Iron Man:  First Sign TPB (basically containing all issues of Avengers and Iron Man between the end of the Crossing and the beginning of Onslaught.)

Unfortunately, most online reading orders do not agree on the placement of a lot of issues in the middle of the event and the comics themselves never presented a clear reading order.  Most “to be continued” boxes at the end of issues basically contained the next published issues of all of the series involved.  Below is a list of chronology or prerequisite clues from several issues, attempting to be as spoiler-free as possible.

Trying to maintain a day-by-day chronology across all four titles involved probably does not hold up. And being a story involving time manipulation, there is some wiggle room for some events to appear out of order.  But I’m trying to keep a logical chronology for individual characters.  For instance, if there is a run of Avengers issues all taking place in the same night, I don’t want to include an Iron Man issue in the middle that takes place during the day.

Chronology/Pre-requisite clues:
Iron Man #319 – starts plans for Avengers reunion “tomorrow”
Avengers #390 – Prelude to the Crossing
Avengers: The Crossing #1 – an Avengers reunion / ends around midnight
Avengers #391 - occurs past midnight following the events of The Crossing #1
Force Works #16 – characters returning from events of The Crossing #1 / occurs during the day, up to “sunset” / opening sequence set at “midnight” is not what it first appears
Avengers #392 – opens at morning, supposedly within 24 hours of the events of The Crossing.
Iron Man #320 – opens on another morning, events of The Crossing were “earlier this week”
Iron Man #321 – references Avengers #391
Force Works #17 – Iron Man explains events of The Crossing to the team as “the day of the reunion”, implying that it is now several days later
War Machine #20 – indirect references to events in Force Works #17, direct reference to Avengers #391
Iron Man #322 - reference to Avengers #391 and War Machine #20
Force Works #18 – has a subplot pick up from last page of Iron Man #322
War Machine #21 – continues subplot from Force Works #18
Iron Man #323 – WM #21 was a few hours ago, reference to Avengers #392
Avengers #393 – directly continues from Iron Man #323
Force Works #19 – Avengers #393 was moments ago, references to WM #21 and Iron Man #323
War Machine #22 – direct continuation from FW #19 / Black Widow and others leave to reappear in IM #324 / main cast continues directly into FW #20
Iron Man #324 – Black Widow appears from WM #22
Force Works #20 – direct continuation from WM #22, runs parallel to IM #324
War Machine #23 – reference to Force Works #20
Avengers #394 – leads into Timeslide
Avengers: Timeslide #1 – continues from Avengers #394
Iron Man #325 – continues from Timeslide
Avengers #395 – continues from Iron Man #325
Age of Innocence: The Rebirth of Iron Man #1

War Machine #22 features two groups of characters working together (one group with Black Widow, one group with Scarlet Witch).  Black Widow’s team leaves and is next seen in Iron Man #324.  Scarlet Witch’s team continues into Force Works #20.  There is a point where both teams communicate via video chat in both issues, but there is no shared dialogue between the two scenes which allows them to be two different conversations.  I’ve chosen to place Iron Man #324 in between War Machine #22 and Force Works #20 for pacing purposes.

War Machine #23 doesn’t have any other references other than taking place after Force Works #20, so it could go almost anywhere after that issue, depending on pacing preferences.