Tax rates for low income / poverty line earners in the USA are lower than Australia, but Australia still has much lower rates of poverty. So, poverty is not caused by tax. There are many other factors to consider.
Poverty line Australia (family with 2 children) - NZD$49,124 per year
Average cost of living Australia (couple, no kids) – NZD$51,829 per year
Tax deducted for NZD$50,000 annual income (single) = NZD$6,635 [13.27%]
Poverty line USA (4 person household) - NZD$35,983 per year
Average cost of living USA (couple, no kids) – NZD$70,873 per year
Tax deducted for NZD$36,000 annual income (single) = NZD$4,320 [12%]
Apologies for the NZD.
The average cost of living in the US is much higher than the poverty line. This is more to do with the lack of a sensible minimum wage.