Russia-Ukraine war: Key things to know about the conflict


              The monument of the Duke of Richelieu, is covered with sandbags next to a Carrousel , in Odesa, Ukraine, Thursday March 24, 2022. The city of Odesa is prepared for a possible Russian offensive. (AP Photo/Petros Giannakouris)
            
              A barricade is placed on a street in front of the National Academic Theatre of Opera and Ballet building, in Odesa, Ukraine Thursday, March 24, 2022. The city of Odesa is prepared for a possible Russian offensive. (AP Photo/Petros Giannakouris)
            
              President Joe Biden talks with Cypriot President Nicos Anastasiades during a round table meeting at an EU summit in Brussels, Thursday, March 24, 2022. (AP Photo/Evan Vucci)
            
              A man walks on the debris of a burning house, destroyed after a Russian attack in Kharkiv, Ukraine, Thursday, March 24, 2022. (AP Photo/Felipe Dana)
            
              The monument of the Duke of Richelieu, is covered with sandbags next to a Carrousel , in Odesa, Ukraine, Thursday March 24, 2022. The city of Odesa is prepared for a possible Russian offensive. (AP Photo/Petros Giannakouris)
            
              A barricade is placed on a street in front of the National Academic Theatre of Opera and Ballet building, in Odesa, Ukraine Thursday, March 24, 2022. The city of Odesa is prepared for a possible Russian offensive. (AP Photo/Petros Giannakouris)
            
              President Joe Biden talks with Cypriot President Nicos Anastasiades during a round table meeting at an EU summit in Brussels, Thursday, March 24, 2022. (AP Photo/Evan Vucci)
            
              A man walks on the debris of a burning house, destroyed after a Russian attack in Kharkiv, Ukraine, Thursday, March 24, 2022. (AP Photo/Felipe Dana)
            
              The monument of the Duke of Richelieu, is covered with sandbags next to a Carrousel , in Odesa, Ukraine, Thursday March 24, 2022. The city of Odesa is prepared for a possible Russian offensive. (AP Photo/Petros Giannakouris)
            
              A barricade is placed on a street in front of the National Academic Theatre of Opera and Ballet building, in Odesa, Ukraine Thursday, March 24, 2022. The city of Odesa is prepared for a possible Russian offensive. (AP Photo/Petros Giannakouris)
            
              President Joe Biden talks with Cypriot President Nicos Anastasiades during a round table meeting at an EU summit in Brussels, Thursday, March 24, 2022. (AP Photo/Evan Vucci)
            
              A man walks on the debris of a burning house, destroyed after a Russian attack in Kharkiv, Ukraine, Thursday, March 24, 2022. (AP Photo/Felipe Dana)
            
              Bell ringers pull the ropes to ring the bell of the Latin Cathedral in Lviv, western Ukraine, Thursday, March 24, 2022. (AP Photo/Nariman El-Mofty)
            
              The general view from the Latin Cathedral in Lviv, western Ukraine, Thursday, March 24, 2022. (AP Photo/Nariman El-Mofty)
            
              The sun sets over Lviv, western Ukraine, Thursday, March 24, 2022. (AP Photo/Nariman El-Mofty)
            
              People pray in the Latin Cathedral in Lviv, western Ukraine, Thursday, March 24, 2022. (AP Photo/Nariman El-Mofty)
            
              Volodymyr Ilnytskyi, 55, a retired policeman, prays before ringing the bell of the Latin Cathedral in Lviv, western Ukraine, Thursday, March 24, 2022. (AP Photo/Nariman El-Mofty)
            
              FILE - A couple embrace prior to the woman boarding a train carriage leaving for western Ukraine, at the railway station in Kramatorsk, eastern Ukraine, Sunday, Feb. 27, 2022. The United Nations says that more than 3.6 million people have fled Ukraine since the war started exactly one month ago Thursday in what is the biggest movement of people in Europe since World War II. Unprepared, most refugees believed they would soon be back home. That hope is waning now. (AP Photo/Andriy Andriyenko, File)
            
              British Prime Minister Boris Johnson, front right, looks toward U.S. President Joe Biden, front left, at a group photo during an extraordinary NATO summit at NATO headquarters in Brussels, Thursday, March 24, 2022. As the war in Ukraine grinds into a second month, President Joe Biden and Western allies are gathering to chart a path to ramp up pressure on Russian President Vladimir Putin while tending to the economic and security fallout that's spreading across Europe and the world. (AP Photo/Thibault Camus)
            
              Children from Ukraine play at an exhibition hall, turned into a refugee center in Nadarzyn, near Warsaw, Poland, on Wednesday, March 23, 2022. (AP Photo/Petr David Josek)
            
              FILE - Border police push an elderly lady in an office chair after fleeing with family the conflict from neighbouring Ukraine, at the Romanian-Ukrainian border, in Siret, Romania, Sunday, Feb. 27, 2022. The United Nations says that more than 3.6 million people have fled Ukraine since the war started exactly one month ago Thursday in what is the biggest movement of people in Europe since World War II. Unprepared, most refugees believed they would soon be back home. That hope is waning now. (AP Photo/Alexandru Dobre, File)
            
              A man walks in front of the National Academic Theatre of Opera and Ballet building with sandbags placed as preparation for a possible Russian offensive, in Odesa, on Thursday March 24, 2022. Odesa's opera house has been called the most beautiful in Europe. (AP Photo/Petros Giannakouris)
            
              FILE - A child refugee who fled the Russian invasion from neighbouring Ukraine with his mother and grandmother plays with a yellow ballon as he lays on a mattress inside a ballroom converted into a makeshift refugee shelter at a 4-star hotel & spa, in Suceava, Romania, Friday, March 4, 2022. The United Nations says that more than 3.6 million people have fled Ukraine since the war started exactly one month ago Thursday in what is the biggest movement of people in Europe since World War II. Unprepared, most refugees believed they would soon be back home. That hope is waning now. (AP Photo/Andreea Alexandru, File)
            
              FILE - A child watches from a train carriage, waiting to leave to western Ukraine at the railway station in Kramatorsk, eastern Ukraine, Sunday, Feb. 27, 2022. The United Nations says that more than 3.6 million people have fled Ukraine since the war started exactly one month ago Thursday in what is the biggest movement of people in Europe since World War II. Unprepared, most refugees believed they would soon be back home. That hope is waning now. (AP Photo/Andriy Andriyenko, File)
            
              Anastasia, 3, is held by her mother, as she receives treatment at a schoolhouse that has been converted into a field hospital, in Mostyska, western Ukraine, Thursday, March 24, 2022. The United Nations children’s agency says Russia’s invasion has displaced half of Ukraine’s children, one of the largest such displacements since World War II. (AP Photo/Nariman El-Mofty)
            A Ukrainian firefighter takes pictures outside a destroyed warehouse after a Russian bombardment on the outskirts of Kyiv, Ukraine, Thursday, March 24, 2022. Ukraine President Volodymr Zelenskyy called on people worldwide to gather in public Thursday to show support for his embattled country as he prepared to address U.S. President Joe Biden and other NATO leaders gathered in Brussels on the one-month anniversary of the Russian invasion. (AP Photo/Vadim Ghirda) A Ukrainian firefighter sprays water inside a destroyed warehouse after a Russian bombardment on the outskirts of Kyiv, Ukraine, Thursday, March 24, 2022. Ukraine President Volodymr Zelenskyy called on people worldwide to gather in public Thursday to show support for his embattled country as he prepared to address U.S. President Joe Biden and other NATO leaders gathered in Brussels on the one-month anniversary of the Russian invasion. (AP Photo/Vadim Ghirda) 
              NATO Secretary General Jens Stoltenberg, center front left, U.S. President Joe Biden, center front, and British Prime Minister Boris Johnson, front right, pose during a group photo during an extraordinary NATO summit at NATO headquarters in Brussels, Thursday, March 24, 2022. As the war in Ukraine grinds into a second month, President Joe Biden and Western allies are gathering to chart a path to ramp up pressure on Russian President Vladimir Putin while tending to the economic and security fallout that's spreading across Europe and the world. (AP Photo/Thibault Camus)
            U.S. President Joe Biden, front right, speaks with French President Emmanuel Macron, front left, prior to a group photo during an extraordinary NATO summit at NATO headquarters in Brussels, Thursday, March 24, 2022. As the war in Ukraine grinds into a second month, President Joe Biden and Western allies are gathering to chart a path to ramp up pressure on Russian President Vladimir Putin while tending to the economic and security fallout that's spreading across Europe and the world. (AP Photo/Thibault Camus)