BREZICE, Slovenia (AP) — Led by riot police on horseback, thousands of weary migrants marched across western Balkans borderlands as far as the eye could see Tuesday as authorities cautiously lowered barriers and intensified efforts to cope with a human tide unseen in Europe since World War II. Leaders of Slovenia deployed military units to support police on their overwhelmed southern border with Croatia, which delivered more than 6,000 asylum seekers by train and bus to the frontier in bitterly disputed circumstances between the former Yugoslav rivals. With far too few buses available in Slovenia to cope, most people walked 15 kilometers (9 miles) on rural lanes past cornfields and pastures to reach a refugee camp, a challenge eased by sunny weather after days of torrential rain, fog and frigid winds. Croatia, which has erected relatively few shelters along its borders with Serbia and Slovenia, directed thousands into special trains and bus convoys Tuesday to Slovenia in an apparently concerted effort to clear a backlog built up since Saturday, when Hungary closed its borders with Croatia. The bloc's border security agency, Frontex, announced Tuesday that EU members had fulfilled barely a fourth of its months-old appeal to provide border guard reinforcements for Greece and Italy, the two biggest entry points for refugees and other migrants. The letter, to be provided to all new arrivals, warned they would face lengthy legal delays and spend a year or more living in "an austere reception, such as in sports centers or tents, where many people share the same lodgings" while their asylum applications are considered. Dutch Junior Justice Minister Klaas Dijkhoff said that given the country's shortage of public housing, even successful applicants might be assigned to long-term housing in converted shipping containers or disused office blocks.