Question: who did the central powers defeat on the eastern front before concentrating back on france
[{'answer': 'the Russian army', 'provenance': [{'wikipedia_id': '9051469', 'title': 'Bulgaria during World War I', 'start_paragraph_id': 83, 'start_character': 518, 'end_paragraph_id': 83, 'end_character': 534, 'bleu_score': 1.0, 'section': 'Section::::The Bulgarian Army.:Mobilization.\n'}]}, {'provenance': [{'wikipedia_id': '9051469', 'title': 'Bulgaria during World War I', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 0, 'bleu_score': 1.0, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14300091318768319707}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '9051469', 'title': 'Bulgaria during World War I', 'start_paragraph_id': 83, 'start_character': 0, 'end_paragraph_id': 83, 'end_character': 1249, 'bleu_score': 0.990171692033262, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14300091318768319707}, 'section': 'Section::::The Bulgarian Army.:Mobilization.\n'}]}, {'provenance': [{'wikipedia_id': '1126912', 'title': 'Waterloo Campaign', 'section': 'Section::::Invasion of France and the occupation of Paris (18 June – 7 July).:First week (18 June – 24 June).\n', 'start_paragraph_id': 70, 'end_paragraph_id': 70, 'meta': {'evidence_span': ['it retreated toward Paris. After the combined victory at Waterloo by the Anglo-allies under the command of the Duke of Wellington and the Prussians under the command of Prince Blücher,', 'it retreated toward Paris. After the combined victory at Waterloo by the Anglo-allies under the command of the Duke of Wellington and the Prussians under the command of Prince Blücher, it was agreed by the two commanders, on the field of Waterloo, that the Prussian army, not having been so much crippled and exhausted by the battle, should undertake the further pursuit, and proceed by Charleroi towards Avesnes and Laon; whilst the Anglo-allied army, after remaining during the night on the field, should advance by Nivelles and Binche towards Péronne.', 'it retreated toward Paris. After the combined victory at Waterloo by the Anglo-allies under the command of the Duke of Wellington and the Prussians under the command of Prince Blücher, it was agreed by the two commanders, on the field of Waterloo, that the Prussian army, not having been so much crippled and exhausted by the battle, should undertake the further pursuit, and proceed by Charleroi towards Avesnes and Laon; whilst the Anglo-allied army, after remaining during the night on the field, should advance by Nivelles and Binche towards Péronne.']}}]}, {'provenance': [{'wikipedia_id': '9051469', 'title': 'Bulgaria during World War I', 'section': 'Section::::The Bulgarian Army.:Mobilization.\n', 'start_paragraph_id': 83, 'end_paragraph_id': 83, 'meta': {'evidence_span': ['Russian army on the Eastern Front. His army group was created specifically to wage war against the Serbian army in the pre-1913 borders of the country ("Old Serbia"), to defeat it wherever it found it and to open the land route between Hungary and Bulgaria. As commander, Mackensen acted independently and received his directives only from the German High Command. However, the field marshal\'s orders to his Bulgarian forces had to be relayed to the commander of the 1st Army by the Bulgarian General Staff, which left room for the latter to intervene when needed. According to the convention, the Bulgarian commander-in- chief retained full and direct control over the Bulgarian 2nd Army and its operations in Vardar Macedonia.', 'The military convention between Bulgaria and the Central Powers laid down the general plan for its campaign against the Kingdom of Serbia. It severely limited the control of the Bulgarian High Command over the Bulgarian 1st Army, which was designated part of a combined German, Bulgarian and Austro-Hungarian force commanded by Field Marshal August von Mackensen. He had recently led the German and Austro-Hungarian armies in the highly successful and victorious GorliceTarnów Offensive of the Central Powers against the Russian army on the Eastern Front. His army group was created specifically to wage war against the Serbian army in the pre-1913 borders of the country ("Old Serbia"), to defeat it wherever it found it and to open the land route between Hungary and Bulgaria. As commander, Mackensen acted independently and received his directives only from the German High Command. However, the field marshal\'s orders to his Bulgarian forces had to be relayed to the commander of the 1st Army by the Bulgarian General Staff, which left room for the latter to intervene when needed. According to the convention, the Bulgarian commander-in- chief retained full and direct control over the Bulgarian 2nd Army and its operations in Vardar Macedonia.']}}]}, {'provenance': [{'wikipedia_id': '51751618', 'title': 'Historiography of the Battle of France', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['he Historiography of the Battle of France describes how the German victory over French and British forces in the Battle of France had been explained by historians and others. Many people in 1940 found the fall of France unexpected and earth shaking. Alexander notes that Belgium and the Netherlands fell to the German army in a matter of days and the British were soon driven back to the British Isles,', 'The Historiography of the Battle of France describes how the German victory over French and British forces in the Battle of France had been explained by historians and others. Many people in 1940 found the fall of France unexpected and earth shaking. Alexander notes that Belgium and the Netherlands fell to the German army in a matter of days and the British were soon driven back to the British Isles,']}}]}]