(Reuters) - U.S. President Donald Trump signed an executive order on Tuesday allowing the Dakota Access Pipeline to go forward, after months of protests from Native American groups and climate activists pushed the Obama administration to ask for additional environmental review for the controversial project.  The U.S. Army Corps of Engineers in December turned down the request for an easement for the Dakota Access Pipeline to build under the Missouri River. Most of the pipeline has been constructed already, with the short stretch under the Missouri River remaining unbuilt. The following is a timeline of the project: December 2014 Energy Transfer Partners LP applies to the North Dakota Public Service Commission to build a 1,172-mile (1,885 km), 570,000-barrel-per-day pipeline to deliver crude oil from North Dakota’s Bakken shale fields to Patoka, Illinois, crossing South Dakota and Iowa, kicking off a year of public hearings in North Dakota. January  North Dakota regulators approve the pipeline unanimously. April 29 U.S. Army Corps of Engineers holds a hearing for Native Americans on the pipeline.  July 25 The U.S. Army Corps of Engineers approves three easements for water crossings for the pipeline at Sakakawea, the Mississippi River and Lake Oahe, which is an ancestral site for the Standing Rock Sioux tribe.  July 27 The Standing Rock Sioux Tribe sues the Army Corps of Engineers in U.S. District Court for the District of Columbia, citing violation of multiple federal statutes that authorize the pipeline’s construction and operation, and seeks an emergency order to halt construction. The tribe also alleges the pipeline threatens their environmental and economic well-being and would damage and destroy sites of historic, religious and cultural significance. The Sioux Tribe say because the pipeline goes underneath Lake Oahe, approximately half a mile upstream of the tribe’s reservation, leaks from the pipeline would be directly in the tribe’s ancestral lands. Sept. 3 Private security guards hired by Energy Transfer Partners use attack dogs and mace after violence erupted at a private construction site along the pipeline route. Six people are reportedly bitten by dogs, a scene captured on video and broadcast widely. Sept. 6 Brian Cladoosby, president of the National Congress of American Indians, which represents more than 500 tribes, speaks to nearly a dozen of President Barack Obama’s Cabinet-level advisers at a Sept. 6 meeting of the White House’s three-year-old Native American Affairs Council. Cladoosby delivers an impassioned request: Stand with Native Americans who have united with the Standing Rock Sioux tribe and block construction of the Dakota Access Pipeline.  Sept. 9 U.S. District Judge James Boasberg in Washington rejects a broad request from Native Americans to block the project. But herules that no construction activity on the Dakota Access may take place between Highway 1806 and 20 miles to the east of Lake Oahe. Construction activity to the west of Highway 1806 may proceed. The tribe appeals the decision. Sept. 9 Less than an hour after Boasberg’s decision, the U.S. Justice and Interior Departments and Army makes an unprecedented move and orders a stop to construction near Lake Oahe until the Army Corps of Engineers reviews its previous decisions and decides if it needs to conduct a fuller environmental and cultural review. Sept. 13 Energy Transfer Partners tells employees in a letter, provided to media, that it is committed to completing the project, citing that the pipeline is 60 percent complete and that it has already spent $1.6 billion so far on equipment, materials and the workforce. Oct. 9 The U.S. Court of Appeals of the District of Columbia Circuit says an administrative injunction related to the emergency motion of the Standing Rock Tribe would be dissolved, citing that Dakota Access has rights to construct on private land up to Lake Oahe. Oct. 11 Environmental activists across four states disrupt the flow of millions of barrels of crude from Canada into the United States in a rare, coordinate action that targets several key pipelines simultaneously. The protest group, the Climate Direct Action, say their move is in support of the Standing Rock Sioux Tribe. As a safety precaution, companies operating the pipelines shut off sections of the lines for several hours while they investigate.  Oct. 25 Government-to-government tribal consultations begin across six regions on how federal government decision-making on infrastructure projects could better include tribal concerns. Nov. 8 Energy Transfer Partners says it has built the pipe to the edge of Lake Oahe and reiterates its intentions to complete the project. Nov. 9 Following the surprise victory of Donald Trump in the U.S. presidential election, climate activists and the Standing Rock Sioux say they still hope President Obama will be able to kill the pipeline definitively. Analysts say the line is more than likely to go through. Nov. 14 The U.S. government, in a joint notice issued by the Department of the Interior and the Army Corps of Engineers, delays a final decision on permitting. They say the permit had followed all legal requirements, but more consultation with Native American tribes is needed. Nov. 18 Energy Transfer Partners’ CEO Kelcy Warren tells the Associated Press that the pipeline would not be re-routed.  Nov. 20 About 400 activists gather on a bridge between the camp protest and the construction path; law enforcement officers respond by using tear gas and water cannons on them in freezing temperatures.  Nov. 26 The U.S. Army Corps of Engineers tells protesters they need to leave the Oceti Sakowin Camp, the primary protest camp located on federal land, by Dec. 5. They later say they have no plans to enforce this order. Nov. 28  North Dakota Governor Jack Dalrymple issues an evacuation order for the Oceti Sakowin camp, citing harsh weather on the way. Officials the next day tell Reuters they plan on blockading the camp so supplies cannot get in. They later back off that plan and say they may just issue fines, but retreat from that idea as well. Nov. 30 A group of U.S. veterans announce they will bring more than 2,000 service members to North Dakota to stand as human shields between the protesters and law enforcement. They begin arriving over the next several days. Dec. 4 The U.S. Army Corps of Engineers denies Energy Transfer Partners’ request for an easement to run under Lake Oahe, sparking a celebration amongst protesters. ETP says it will continue to fight for the line. The incoming Trump administration has said it supports Dakota Access, along with other pipeline projects. Jan. 18  The Army Corps says it will publish a notice in the Federal Register stating its intent to prepare an environmental impact statement for the easement at Lake Oahe. ETP files a motion asking a court to bar the action in an effort to move the pipeline forward. Jan. 24 President Trump, who previously owned stock in Energy Transfer Partners, signs an order aimed at moving the pipeline, along with an unrelated pipeline, Keystone XL, to go forward.  
Factbox: Dakota Access Pipeline's long journey