CINXE.COM

<!DOCTYPE html><html lang="en-US"><head><title>Just a moment...</title><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=Edge"><meta name="robots" content="noindex,nofollow"><meta name="viewport" content="width=device-width,initial-scale=1"><style>*{box-sizing:border-box;margin:0;padding:0}html{line-height:1.15;-webkit-text-size-adjust:100%;color:#313131;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,Noto Sans,sans-serif,Apple Color Emoji,Segoe UI Emoji,Segoe UI Symbol,Noto Color Emoji}body{display:flex;flex-direction:column;height:100vh;min-height:100vh}.main-content{margin:8rem auto;max-width:60rem;padding-left:1.5rem}@media (width <= 720px){.main-content{margin-top:4rem}}.h2{font-size:1.5rem;font-weight:500;line-height:2.25rem}@media (width <= 720px){.h2{font-size:1.25rem;line-height:1.5rem}}#challenge-error-text{background-image:url(data:image/svg+xml;base64,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);background-repeat:no-repeat;background-size:contain;padding-left:34px}@media (prefers-color-scheme:dark){body{background-color:#222;color:#d9d9d9}}</style><meta http-equiv="refresh" content="120"></head><body class="no-js"><div class="main-wrapper" role="main"><div class="main-content"><noscript><div class="h2"><span id="challenge-error-text">Enable JavaScript and cookies to continue</span></div></noscript></div></div><script>(function(){window._cf_chl_opt={cvId: '3',cZone: "publications.waset.org",cType: 'non-interactive',cRay: '9134c6cb5b77fce3',cH: 'qhhHEsq5SvNoSnn8lVPdro_m3t5Q4wqEAvf.AuUI_ck-1739784813-1.2.1.1-S_NRPPIl1cxTDglAwYmzM0xG_bB4NBoPsbDXfwUTj7TFlRzTyQFTaXhJ9CVQvlmz',cUPMDTk: "\/search?q=twenty-first%20century.&__cf_chl_tk=9PwW1TELcNZ6aE1ICsdhz0dECKxayLc0odvI1xrMaTc-1739784813-1.0.1.1-7VxULgruvrnRNHGjE23qJvk4AXLkzCRINVxvQTFnbUI",cFPWv: 'b',cITimeS: '1739784813',cTTimeMs: '1000',cMTimeMs: '120000',cTplC: 0,cTplV: 5,cTplB: 'cf',cK: "",fa: "\/search?q=twenty-first%20century.&__cf_chl_f_tk=9PwW1TELcNZ6aE1ICsdhz0dECKxayLc0odvI1xrMaTc-1739784813-1.0.1.1-7VxULgruvrnRNHGjE23qJvk4AXLkzCRINVxvQTFnbUI",md: "Ns.eHN4hCdQtl6qIjfycf8s_3Vt9sZMsutQMkujjjOI-1739784813-1.2.1.1-iWNgGRuEXND81xs1Z7KqRqiNT_l.vJhsY4tdcyC.PoiCXSPqjiaWP8nsfquSJ5LeB.eE0GogAhWwnpmf67cb.rK9mD5sD.VM6OzmDhRrkofNf6gwkrFLU75Go_yo_WRvCEG99DquXgpSTOudJ8Kxs9wKpAEUE.b.TI3Gk9bPh2HUmo9ObtGY1GuAatdC89e_DQ2LotFJ6fNffLcrF2jjpksy11HEH8ePm243QE1.zaJYNasKf9tMcBIs4KMOcbfpkX068Sfw1CfxIh4PpWpMEfHkuNUkvHOT6WAA7l3dzlvC1JqhfBCoFIPe30Y1K1WXJaLyDVt7tBY6EiH2EoI_9CvuDeShMiz9fJeeBzmLkhsqOFkiG3NyoSkNUSKR.kKuSbBCjMuc2LfiJ6FntyI48.4n2KVSJ4MVGUS4WhlbcSI57aLa6puZ1WFlcesz2TrQwlvfBzukZseCxruF5ljP1SmDq7wsyDvEdKIbr2l1NqI7cwf9WMtktFn5TihOla4hgg6wJoSv4Jp8yJz6mGX9kq8hvSIXeWUFLCGHpNS6.A_SkiIDkRXxtwWb59nSWBebyRcFZKlEhQ41gQcmmBqUMn6uIj9m_KvVfHaz26SxmATaVcfkTJ6y3W_BkirfIEYuCyjqiM8CZWailUJrGwuEViUM6XO8dEP0cXTtzvFk0c9G7WUwJCMmGuIZWlKrRZyF0Gss2X3s.wKAWLqw.zKWwek734VwgJXSKdkb_kB8fjaVxmFF3HgCjmdaIDjwV5uIMIA.6wcyViAVfCEuYMuwOvz52e4WL_qSZz048_jrEHBMZkpldboTlTtsR4oN68kgst7NGbnknoLTotyGr7NEWvAEZslp7d9iUe.6gBbI92qZxp91VRynAIdWgJ9yWy479ezIa.uGQ2wpkkoJs3bd5byENKgbupEemVc_8C3elyJ5XOx42Z.jTgVC48dQkIbtJrGBk4yzyEvkRZ9Xv4ocdkuK4D24N0A88UFD9Ug5_44tT37Kjn6cHmb0jyeTX7PFMNMdORUZZQwPeEthJsPVTppEKcL.PYSSLucxZZInjOxDgMaP.cUd4H.Eruh6vFdrTh1lFt4_zPQszeIAeER7p_rezBeM99814.IOH_TfXJPvIV35gtQmev42JwPRG5YftyQNJQcOdeO9mz7xACct3Vb3biIUZhRIlWNjhea0QmfKToinpo4XDzSiv.SJ6mW4JP4SPXW6iLdwFHqrFVVoKavNDOCPTh9ZW9kjVAeQwifI5Rb71HcIGnhaKn1f.SyOjawrQIEkFZIJS2egxioS8kKcDF4cpIjfUceRSJPrEOozTDwbhLDhu8w46NXMQ1Jj7pomFdpUUTymPoesL_NX6O_yO2I3yFfM_ijAPiqUAvWqRsjMJzCk0rUSCrlCsucnVm5ZSo.wCOs17QkjnFdX6l5CpBojCpgZXeJPIwPeSpBJCHZW.EUtfUnopxasf3RJA2eqNfhM2vAzUN6OCiu67kCg7PgmNf4pSHk8L9Do1goYMBJjKVfynQ5TbI8p8GazBw9RG0IUuSIcOj27CgqEb.C_NZEqlcGxXSIiTyAD7Lq58qhpyj8f2.HoUvQ6i8rtq_4NesAkqcQVMrLBNF6KPHeWn.KCV50Z.oR5YDT.9i0Y4xmxC9JzvvrcbAsjhnOGyUEZ_AR2.CfibI4U9IcQPwyBwCGA42YN_.51OH8JidKqfcRgVLuled_96EZB5TRmiKl0zgtNk6WYMgBCqgpxCJib0r_m8wZQKLk3nDjHkx8GmBfqOlq0.FATUU2oFTCRZiCup9.VadgtyDGE3Fp4xA7Lj82VFwxdLuPkPHOodyBDVor45lvM.NPkyEB4_mvF7v8BIApWHHs7Qs3RccX3SVj0n5CqMI1yVOuTs.XD43WQVEYS.dL9tJWHqlGffqPBOMn.QpgwVYyjxJKUD2ja_yVV6IWFv6rRxilai2vgWK8",mdrd: "9K5RKD4eTipiZPoymxA80uURoqzeklyrT9pfvM8MAMc-1739784813-1.2.1.1-G8vtEGmJTrOr_sbsBkFQhd9fVUiWlMAcaW6KtYwiql_1QMeOaotPDSQLqj5cmHHSwXG_0L4WGkBpAS4gsAEDeEm5178ExpUSLuBm.BnonfPEpovRChHVjf8bzxXtHOen8vsUb5H5Ki1WUkYGRTd8FYY_bGsP6A1jEdn9orSOtqyo3y9HG2ZKxZm6FfNGn5GFlv8pX0oReucRxb530dZ1d.sAqZFu2pBCkFSAY3r00XrkXLxF7EUhE7xsY965X.58jMZIXy77CIftw1qPaVT6K3jsnPESprahg6HsQw9CIJIoMuYxeMOgWvflfesTonrBjhcAOGftZk2xDB9cuQJVmtPjpj3_RIqZPR.vBCBM8skEmXyur4bqI9WoX1nqUVk6IpgdmAw8ocDTf_BTXdi4sq4mjfLHaPwKOyZV_AquKWC1isyqFOKyEofJR48zcZaizwQq63kmBlr1Mo9vK8FToly7qYeZETEuctvHlcUv88JkG1F2e.C4lzAKMHAIZlutNlmeSa9WaLgHF2ajthaun0VNMhb6cF2fO8ZjfmUMokUgPwgGgPyzxw_DvTRLN9ALkRMD1xPpCBo0ohregNt2BNjVazyG5CkyL1WtdWQ2F9f97IgRd.a0HrkDQ665gRLK6WCRnoCEq7DeutSO4OtbFMNEuQeF3jMbHTXvjz0z.nIQyw.JY9bzftS6spICXpehQh_WPhwDaDR2rX.gNojczrU7L7in5JAldYg792Yk93OzqIOHjVdOeOqcem7ezzofdtHVtQybaCifnyDeQs11IF7HBrm7PzKoCgKBQvQO5_9EKLJxLnhNOJc6ODo2C7AZ.rOs07h2M5iMQDhPReRxOHrAz1ftQmaKW5gb1wsmiWEdY5.pEmAScGnD3Dtd_Vh3wVUBhJAPRphkUMBfTeiF1GXrhqps6xvhqNzypvgX9kz.RaFdEuVLGDXs928mNgTtsZMqjiNDf1vNGQhtIT58kDE.LavM3FD51VYtuKfsmbqv2YszciPdrt6Pl.3kNCAcD4UOrRb6u1NbihaU4JtTCxPZqLW16LlJCzrBbjzv5MyA7mn3QofBK2gjzqkZd3tqXZ_5HSwmk8zE8crPNDGwHDhrKKyoOpdcBHQ7K4KbPvfJjDoOo3ncYRMk_2uj.uUYvVvOAnzzGJ_UcDMdS51h8V4i12OYYZMc051cP9tlXJaAsFQMRLb4_Ln_SGVWs3N2kwdWcOx6j4JQcKzd9PI3zId3j.RcWT85wie4JSczbIVEKQmS9Alvl72yPkxMnk1jUAr9BjhozsfeT5v8FmxUKAKKZa7tPiGYqHjxC1jFUda1h_hbD2MxUC4TPUJfY13H_iWFy6stqgQeox2ZdfNEb.LimLkLQuBJXLk2IDiUw2CXY1CjlTV5t3KkpSREhFQx9CczjQQcMWT0nEDMR5_t8nLcN88EzFpSvkF4uSFe7gRe5sUREClWTcZSppWkkknNnZagsomRpq1Fp1sjd1sjrixlsqUtQHrS.jNEG5KPVdb0Lq23h5EcvLn1h42YlzJAZSGDG0pzNXHcv6vU_XD8SJeGqUoY1NTxoUPgPH5kO_Q4nSCQ_F7AhIDWBC4zpPmfLro4lflg7IT1.AKZhIFH9WAdiEaqSVLrBzcCwo0He9.zcnGbfwNhrdlF3RxWgtTo5ThsEHb13uiXWMC9pfHncU8sxPpj.mFeWqbRis2xdYt.QIEH0MHzYvY4wQE__JZA4T8Ge3S30mC9b.Z_koL8DzNbSaPh8T9rmnhRarYXlEem27HxsxGzMvthENB2eVsucJXvtRjWPgClHDDNryHGlLUnVnK1BvE9J3KBHawiknD699uk3s6Zsgzqqta0Pn1D3xhKQpfxTDk20tPcQ9745Axfse4OHFRw1M_k7NARzlVqgy7c2J8DslkxseFbblez_DHQpDCNXR.w_7Nqeuw7qTVt17X8aZ5vv4_MBUI7REksRkmcAqPBFcCKl98FyMyQyGS9MyUNn4A5RHm5d4uu5g"};var cpo = document.createElement('script');cpo.src = '/cdn-cgi/challenge-platform/h/b/orchestrate/chl_page/v1?ray=9134c6cb5b77fce3';window._cf_chl_opt.cOgUHash = location.hash === '' && location.href.indexOf('#') !== -1 ? '#' : location.hash;window._cf_chl_opt.cOgUQuery = location.search === '' && location.href.slice(0, location.href.length - window._cf_chl_opt.cOgUHash.length).indexOf('?') !== -1 ? '?' : location.search;if (window.history && window.history.replaceState) {var ogU = location.pathname + window._cf_chl_opt.cOgUQuery + window._cf_chl_opt.cOgUHash;history.replaceState(null, null, "\/search?q=twenty-first%20century.&__cf_chl_rt_tk=9PwW1TELcNZ6aE1ICsdhz0dECKxayLc0odvI1xrMaTc-1739784813-1.0.1.1-7VxULgruvrnRNHGjE23qJvk4AXLkzCRINVxvQTFnbUI" + window._cf_chl_opt.cOgUHash);cpo.onload = function() {history.replaceState(null, null, ogU);}}document.getElementsByTagName('head')[0].appendChild(cpo);}());</script></body></html>