http://www.bungie.net/Stats/Reach/FileSets.aspx?player=The%20Zip%20Zap%20Zop&set=47690

Halo Reach: End of Days Campaign Gameplay Trailer - YouTube

World Events
December 28th, 2019: International tensions that had been on the rise finally snapped as North Korea declared war on South Korea, and desecrated everything within 50 miles of the border with their massive mortar assembly in a brutal surprise attack to follow the long and coming declaration.
December 29th, 2019: The vastly superior South Korean Air Force retaliated to disable North Korean artillery stations and target population centers. However, they were opposed by massive amounts of unexpected Chinese fighters and routed.
December 30th, 2019: U.S. Armed Forces are quick to enter the area, due to the massive tension between the U.S. and China, finally a chance to pay off the "unique" debt that had formed in 2013.
January 3rd, 2020: With the massive U.S. Military, Air Force, and Navy at their back, the tides quickly turn and the South launches an Invasion on North Korean soil.
July 18th, 2020: The massive joint U.S. and South Korean Air Force overruns the Chinese fighters and bombs away the North's numerical advantage.
July 31st, 2020: U.S. Forces locate rudimentary North Korean biological research on protein mutations. They secure it and quickly send it back to the continental U.S.
August 2nd, 2020: The U.S. Government quickly begins research on the Korean protein research, shrouded in secrecy. The research is carried out aboard a submarine, off the coast of Cape Cod. The sub is armed with a multiple failsafes and containment measures, the final line of defense being a nuclear self-destruct.
November 8th, 2020: The pseudo-proxy war between the U.S. and China finally breaks into an all out war as China attacks surprise attacks the U.S. 9th Fleet, anchored in Japan, totally destroying it. At the same time attacking U.S. forces in Korea, however failing to wipe them out with the same efficiency.
November 9th, 2020: After routing the attack on the Korean based forces, the U.S. wasted no time in retaliating, choosing to launch a heavy counterattack with assets already in South Korea while at the same time moving massive amounts of troops and Navy assets to Japan and other near-China locations.
November 12th, 2020: China attempts to move the fight away from their territory by launching a series of massive blitz-style attacks into the American forces. This continues for one year, a massive push and pull across the West Pacific, often known as the "Second Pacific Campaign".
December 21st, 2020: Chinese espionage finally reaches deep enough in the U.S. Government to locate "Project 246", a U.S. Government biological research project centered on a submarine off the coast of Cape Cod.
December 22nd, 2020: They find that the U.S. Gov. had located a highly dangerous protein which is only present in about 2% of the human population. It's effects, however, are adverse. It converts people to infect others, as the protein released chemicals into the body which can reproduce the protein mutation if transferred to another "host" body. The effects of this were sheer biological instinct to spread the protein to other humans, as it failed to convert animals and insects; it simply killed them.
December 14th, 2021: American forces gain enough of an advantage to launch an attack on the Chinese mainland.
January 17th, 2022: The U.S. Task Force secures itself on the Chinese mainland, a distraction to cover the upcoming attack.
January 20th, 2022: American Air Force and Navy forces used their massive superiority to wipe out the massive Chinese numerical advantage.
July 21th, 2022: In a last ditch effort to halt the American advance, the Chinese begin reverse engineering the mutated protein in the Mao Defense Shelter.
July 30th, 2022: The U.S. Military defeats the Chinese at the Battle of Hong Kong.
August 15th, 2022: Research in the Mao Defense Shelter reaches a breakthrough and the discovery is made that protein is triggered by a unique strain of rabies codenamed 'Creeping Death".
July 18th, 2023: Shanghai is captured by U.S. Forces.
July 19th, 2023: China officially falls to America. Chairman Wong is found and executed by U.S. Forces.
September 20th, 2023: The Mao Defense shelter loads the payloads of the virus onto several ICBM's, and launches them at various targets in the U.S. mainland. Shortly after the launch, U.S. Forces attack the fortress, entering and destroying several hundered units of the virus. However, the Chinese survivors self-destruct the fortress, killing the U.S. Forces and them alike, launching more of the virus into the atmosphere.
September 21st, 2023: The ICBM's come back down on various targets. Some are shot down, which spreads the virus into the Mesosphere, causing infections worldwide.
September 21st, 2023: The outbreak begins.

The Survivors

Slightly stronger than the infected, however can be downed quickly and are still vulnerable to assassination. Watch your back and make sure you have a gun, it won't take too many hits before you're down, and there is a lot more of them than you.

The Infected

Normally weak alone, it won't take too much to bring them down, however what they lack in strength they make up for in stealth and numbers. Always aware of your position. When they start charging en masse, you'll find yourself one of them real fast if you aren't prepared.

Objectives

Survivors
Your goal is not to camp and get as many kills as possible, but rather survive until time elapses and/or reach the end of the level. Whilst there is a kill scoring system, this is supposed to played as a linear level, like you would find in Left 4 Dead's or Halo: Reach's campaigns.

The Infected
Simple. Kill all the survivors before time elapses or they reach their objective.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=27039726&player=The%20Zip%20Zap%20Zop

ACT 1: EMERGENCY - Halo Reach Infection Campaign - YouTube

"30 minutes ago, a patient with a unique string of rabies was moved to the ER. He then went berserk, infecting three people."

Act 1 is a CQC map set in a hospital with a creepy, desolate environment. An infected arrived at the Dornbecker Hospital in Philadelphia, spreading the infection around the building. Survivors barricaded themselves in the lobby and operating rooms.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=27040522&player=The%20Zip%20Zap%20Zop

ACT 2: HEAVY CASUALTIES - Halo Reach Infection Campaign - YouTube

"The infection has already spread around the state. FEMA has failed to save the survivors."

Act 2 is a large-scale Rifte-esque journey map which is set in a metropolis overrun by the infection. The Infection from the hospital and various other infected has spread around the state of Pennsylvania. Surviving Police forces from the city of Philadelphia are attempting to reach the local Army Recruiting center for weapons and possibly other survivors.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=26360348&player=The%20Zip%20Zap%20Zop

ACT 3: ON THE DEFENSE - Halo Reach Infection Campaign - YouTube

"FEMA has failed, and the US Military has been deployed, but are being overrun. Hold the line."

Act 3 is set on a large cable-stayed bridge, where the military got caught by infected while advancing on the city. The Army took a beating due to the sheer number of infected and the lack of effectiveness from bodyshots. Scattered survivors are trying to hold the line.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=27040684&player=The%20Zip%20Zap%20Zop

ACT 4: THE HARDER THE FALL - Halo Reach Infection Campaign - YouTube

"The Air Force is making evac rounds along the East cost. Task Force survivors are making a push up the Dunwhich Tower to evac on the roof."

Act 4 is a massive journey map, set in a derelict skyscraper in Philadelphia. Task Force 440 after narrowly escaping death at the Bridge are making a push for (temporary) safety of the U.S.A.F. evac forces.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=27040802&player=The%20Zip%20Zap%20Zop

ACT 5: OUR SHIP IS BEYOND SAVING - Halo Reach Infection Campaign - YouTube

"The pilot was infected, and crash landed on the USS Truman, just off the coast of Maryland."

Act 5 is another enormous journey map set on an Aircraft carrier during the late stages of the war. Infected are everywhere, even at sea. Task Force 440 re-groups and makes a push to the torpedo bay to destroy the vessel.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=27040803&player=The%20Zip%20Zap%20Zop

ACT 6: DEFCON 1 - Halo Reach Infection Campaign - YouTube

"DEFCON 1 has been declared. Defend D.C. at all costs."

Act 6 is set in Washington D.C. as the ultimatum in the war begins. DEFCON 1 was declared, and missiles are in the air. Task Force 440 survivors and making a desperate push to the capitol building, where a derelict fallout shelter lies. World's ending.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=27040870&player=The%20Zip%20Zap%20Zop

ACT 7: TOTAL ANNIHILATION - Halo Reach Infection Campaign - YouTube

"The missiles that were launched are coming back down... You'll know when it hits."

Act 7 is a journey map set in a fallout shelter during the nuclear attack on infected. Several devices struck D.C. directly, the closest being directly on top of the Jefferson Memorial. Survivors are making a push into the overrun fallout shelter to survive the hell on Earth.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=27040931&player=The%20Zip%20Zap%20Zop

ACT 8: END OF DAYS - Halo Reach Infection Campaign - YouTube

"Nowhere to run, nowhere to hide."

Act 8 is set in a post-nuclear Washington D.C. after survivors emerge from the fallout shelter and find the attack wasn't as successful as hoped. The Eastern half of the continental U.S. is a radioactive ruin. CIA and Army survivors attempt to hold the Capitol Building, but are failing...

Strategies
Survivors

Remain in groups. This is key, because alone the infected will pick you off no trouble.
Keep your head on a swivel. The infected can come from a myriad of places and if you're assassinated, you're dead.
Watch each other's backs. Assassinations are one-hit kills and you lack radar.
Make sure to always have a gun. Using a sword may be tempting but you're going to lose health with each encounter with infected and become one of them in short order.

Infected

Attack in groups. The survivors will have a much harder time in defending themselves, as charging in alone does nothing.
Utilize the environment. Rooftops and buildings are great cover, and the survivors are one-hit kills with assassination.
Use distractions. Out think the humans. If they are all busy shooting at a group of infected charging straight at them and you sneak in behind unnoticed...

Fin Act I