What is the main conflict in Between Shades of Gray by Ruta Sepetys?

Lina Vilkas is fifteen years old in 1941 when a group of Russian officers beats on the door of the family home. Her mother answers and the officers rush in, placing the family under arrest but without any information why they are being targeted. Lina, her mother Elena, and her younger brother, Jonas, are taken to a railroad station with hundreds of others. There, they are loaded onto train cars and left.