Russia’s invasion of Ukraine four years ago launched Europe’s biggest conflict since World War II. It has caused immense suffering for civilians and harrowing ordeals for soldiers while rewriting the post-Cold War security order. The fighting enters its fifth year on Tuesday. A U.S.-based think tank says that as many as 1.8 million soldiers may have been killed, injured or missing on both sides. Another think tank says Russia controls nearly 20% of Ukrainian land. The U.N. says at least 14,999 civilians have been killed in Ukraine.